battery health myths, till what percentage should I charge my phone?

I got a new iphone for the first time in my life a week ago and ever since everyone been telling me to do this and that to preserve the battery health and how if my battery only stays for one day for me that means my battery has a problem ( I follow the 20%-80% rule and I only once charged my phone to 100% since i was told to do it for the first charge?) Im constantly thinking if Im doing anything to damage my battery, I read every comment about battery health and probably watched all yt videos about and I found people not following the 20-80% rule and theyre doing great, i really don't know what to do, I also realised my iphones battery drops slower from 80-50% but from 50-20% it goes down a little bit faster is this normal?

should I stop this 20-80 method, is it really hurting my battery? should I charge my phone till 100%? any tips?

(Im overthinking a bit too much)