I am not having all issues as you told but Camera performance was an issue for me but for me it resolved with Android 10 update. You shouldn't worry about RAM usage it is same for my A50 and new operating systems like android, are pretty good at RAM management. More free RAM doesn't mean better performance. But as you are saying that you are having app delay, game lag, heating and screen flickering issues , I would like to ask that have you debloated your phone? It is very important for samsung phones if you want good performance. But if there is no bloatware on your device and still facing these issues than chances are that something has went wrong during update. Have you tried hard reset?
I also read your another post about volume on JBL Endurance and I would like to say it is the problem I would like to be fixed as soon possible. I didn't know that someone else is also having the same issue.
I don't own any Realme device but I would like to stay away them, not because they are chinese manufacturers but because of their privacy invading policies. I don't think that samsung is privacy friendly but i find it less intrusive than other manufacturers. Though I have listen many positive reviews of Realme from many friends.
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