I feel like the RAM plus it let around 60% of app keel running at background even you press back button,
Before android 11 when we press back button app is close, mean not running, unless we press home key
But android 12, one ui 4, most app regarless built in app, third party app, there is not different press back or home button, system still let it running background,
So when run out of RAM, system will trying kill half backgound app, that will look slow down, when you open app
Suspect is RAM plus function
Sorry long screenshot below
Before open other app

After open some app, i press back button, not home button

Why stupid running backgroud?
Here RAM plus description

If anyone got old samsung phone with android 11 below can try, just few built in app will stay backgroud when tap back. All other app will close when tap back button