Just ignore it.

yes

I actually don’t accept or decline, I let it sit there in limbo forever

I'm not really on social media much now so I'd have plausible deniability to say "oh sorry, I didn't see it, I'm not on there much." And if it's not someone I see regularly I wouldn't feel badly about declining

Mostly yes but sometimes I will sigh really big and accept but unfollow them.

Well, if I don't know I'd probably accept. Though depending on what social website, I may not accept anyone I don't know.

I sidestep all of this by (mostly) staying away from social media

I don't know, that's why I left Facebook.

First I make sure I know why I do not like them or if I really do not like them. When I am sure I want no contact then I decline the request. When in doubt might wait for a while. But there are requests when I have good vibes and readily accept asap.

Yes, probably. But then, I might decide I kinda like them just because they wanted to send me a friend request.