I feel like I've answered this one multiple times, in increasingly obtuse ways.
When I have an idea for a whole fic I just write the very basics of the scenes in notepad, so I have some idea of what needs to happen to make it flow. But I also make random assorted notes in other notes apps if I have ideas for dialogue or whatever and I'm not at my computer.
I only have 5 WIPs right now, but I do have basic plotbunny files for a few other random fics. Mostly crossovers that I'll never get around to writing - there's a couple of Worm crossover ideas that are just "these are other franchises I've never seen crossovers for despite obvious plot implications" and nothing else.