hi! this is such an interesting and difficult topic. as a reader, i think it depends a lot on your ability/willingness to ignore certain things? we probably all have certain pet peeves, depending on what we're knowledgable about and familiar with! and of course the delivery of a story matters, as do the expectations we have for them. someone writing fantasy is different from writing fic set in a realistic world. but even then it's fiction... with fanfic especially i don't expect anyone to do the kind of research someone might do for a traditionally published book!

the question probably is: does that truly take away from your enjoyment of the fic? you have a lot more power as a reader to ignore certain things than you might think! and still it makes me anxious when e.g. someone writes about a characer being bitten by a cat and it's treated as a regular non-threatening injury that doesn't require medical attention. (cat bites are dangerous, please see a doctor if you can.)
then--are they perpetuating actual harm? also depends on how popular their fic is.
in how far unconsciously do and consciously should we let fiction inform our opinions and actions? this is a highly debated topic, and i think you should find your own answer to this. the one thing i find worrisome at times is that fanfic is most often inspired by other fanfic... it's a weird circle, and we repeat things we have seen in others' writing to a great extent. sometimes it's a matter of wanting/needing to fit in and it being how things are done. think about a lot of tropes playing out a certain way in the majority of works. think about smut--there definitely is one "official", or maybe more like... traditional way to go about it, like it's some kind of secret code or language you are supposed to pick up on and that readers expect you to speak. and in this case it again is mostly a matter of--do you have expertise in this? do you see your experiences reflected? is it fun anyway, and what do you want from smut, and in how far do you want it to deviate from (your bodily, experienced) reality? and not to mention the writer's intent. and all these can coexist with the fact that most people do not bother to learn where prostates are located and that they're in finger's reach (and even without penetration!). is this annoying? oh yeah! does it do any harm? not so sure tbh lmao but probably also yeah. would it hurt writers or their fics to not write prostates as if they're deep inside someone's body? absolutely not. but again, what you make of this is your decision! what worries me personally more than people getting stuff wrong is--when someone "violates" this traditional "code" by adhering to biological realities that also align with their own experiences... and then getting harassed over it--for writing it the "wrong" way.
i picked this example because it also is something that few people receive adequate education on--for people who (want to) have certain kinds of sex, fanfic might actually be the one source, next to porn. idk about you but my sex ed was firmly concentrating on basically pregnancy 101 for cishet m/f couples (and even that's a Lot of sex ed for some people). it's of course not a singular fanfic writer's responsibility to provide sex ed for anyone! my issue lies more with the fanfic smut culture itself i guess that is unquestioningly reproduced--and does sometimes also feed into (cis)heterosexist stereotypes about men who have sex with men (e.g. the absurd focus on penetrative anal sex). i am a gay man with a fundamentally different lived reality from this, so this is something that--while i don't see it as overly harmful in the grand scheme of things--does annoy me and distress me at times, mostly because nearly all smut shows me that there's no room for gay men like me? as you can see this dips into the lack of having one's existence acknowledged, so somewhat existential questions now. it's a very complicated topic for sure!! so yeah sure i sometimes wish people who dedicate a lot of their time to writing smut would at least type some things into google once and look at the first two or three reddit threads on it, if they don't want to waste a lot of time.

all that said--i'm probably on the same page as you. if i bring up medical conditions, i will at least do the minimum research (skim one or two articles from professional resources) unless it is a lived reality of mine (and even then i might do it). i wouldn't think of this as a reflection of someone's skills or dedication or anything--and i wouldn't judge anyone for skipping this, time is precious, fanfic is for fun--but more of my personal level of comfort to make sure i don't have glaringly huge issues in my fic. i'm probably more on the overly cautious side of things here! i once looked up statistics for the most sold cooking oils in sk for a throwaway mention, and i'm like navel-deep into researching seals for a selkie (= fantasy!!) fic. i think being both a slice of life writer and someone who recognises that it is fiction but also can't and doesn't want to separate their politics from their writing informs how i feel about research. i do feel a sense of responsibility to do my best not to write things that could cause harm or perpetrate certain -isms, and also try to write things as close to life as i can, although no one would come and bug me about the details of my slice of life vs. something with an effect on actual people that i would definitely need and want to un- and relearn.

that said--it sounds like you could use a reminder that it's just fanfic? if it gets to the point where you stop writing because of it, maybe you could just use a simple disclaimer at the start of your fic and address these things. just say you're not a medical professional and ask your readers for their suspension of disbelief! i value that kind of honesty, and i think it helps connect with readers. maybe you could also stick to simpler concepts, a lot of fiction glosses over the details of medical things and focuses on the effects and the emotions--that's usually what we're here for! like, don't overdo the research, it's probably not necessary, especially when you feel so cornered by your lack of accuracy (that very few people might even notice). you're not writing for a medically educated audience! people should not judge your work by that alone! your fanfic is probably about something else, at the core. maybe you're focusing more on achieving perfection (which is... not something you should be striving for, there are so many more things we get from writing fanfic imo and you will always disappoint yourself by not achieving it) than enjoying the writing process? sometimes, i take this as a sign that i should find a different way to achieve whatever i want characters to go through. depending on how you write, this could mean a lot of issues with a plotted out draft of course... but it's still worth considering. another solution would of course be to get a sensitivity reader whose personal experiences could also be worked into your fic, but idek if people really do that with fanfic, and it's a lot to ask from someone without compensating them for their time and labour.

it's really about where you personally draw the line--and whether your readers happen to be the kind of reader who knows more about the topic you're writing about than you do.
as readers, i personally think we should extend as much grace as possible towards writers, always, in most regards (really harmful or violent stereotypes aside), and concentrate on the things we like about a fic or someone's writing as well as keep criticism of this kind out of the comments (and generally everywhere fanfic writers would see it, unless explicitly asked for). and lastly simply move on to other writers if we find ourselves repeatedly uncomfortable with someone's writing!

i am SO sorry this answer turned out to be this long (i should probably pay you for reading this...). hope you found at least one thing to take away from it ;;; and tysm for asking!!