It's when corrosion sets in things get unfixable. If you get to its insides before then some IPA and a decent scrub with something like toothbrush can clean it up.
The exception to this would probably only really be the battery and yeah that should be disconnected as the first step.
True I've had screens on smaller devices go very distorted for a few days after ipa was used elsewhere. They did actually clear and go back to normal mind you and I've never actually went near an actual screen with ipa intentionally.
I get it, ipa is good and fixes surprisingly a lot but only ever use it on boards, components and things like buttons and connectors. Keep it away from screens and batteries.
I've always done this honestly maybe I didn't explain well. It does do a miracle job on water damage if done early enough though.