I imagine this can be tricky if you’re in a home with kids as managed users who keep trying to guess the PIN of your admin account (and all of a sudden, you’re no longer able to sign-in as that admin user). I guess it might be a different story if you’re talking about regular accounts inside your Plex Home (though IIRC those don’t sign in with a PIN).
There’s been a feature suggestion from some years ago which was discussing an option to increase the waiting period to retry after every failed PIN entry. It’s definitely a different approach (and didn’t maintain any attention over the years)… just throwing it into the pit in case this is in line with what you’re looking for (in which case it might be best to keep things focused in a single thread).
My idea is more if you have too many try on a account of one PIN, you block the loggin account only for them account. Or block this account to connect to the user where them try to connect.
I hope my idea is clear. But they are more if one count are compromise in the plex home, it can’t connect to the admin account.