My iPhone stuck in a certain battery percentage

So i updated my iPhone 8 plus last september 17 (Ios 14) so when i updated it i noticed my phone was charging very very slow and heats up while charging so i keep hard resetting but the battery percentage goes down and then ios 14.0.1 it fixed my slow charging but when it reach to 80% - 85% it charge very very slow again. Sometimes it’s stuck in 86% so i hard reset again and it goes down to 70% and i wish app optimization in other apps like tiktok. Only tiktok app really heats up my phone so bad so when i go to shoot it lags so bad. Btw i used original apple charger since 2017