Guys, this situation is very frustating but finally there is a SOLUTION that I have found recently was a local non-official repair store that applied thermal paste inside my iphone 12 over the CPU, the device feels hotter in my hands but the technician guy told me that now the excessive heat trapped inside the phone is dissipating through the mid frame and back glass, stopping the CPU from throttling, performance is way better than before. The waranty is void, but i dont care, i paid a lot for premium performance, Apple was just ignoring this and no update have solved the problem, I guess my next phone is not going to be an Iphone... Apple could have fixed it by just adding a simple heat pipe like the other flagships....

Update: After managing to see the FPS using computer I realized that the FPS is not the problem since all the tested games seemed to be running at contant 60 FPS, so performance of the CPU/GPU is not the problem.

I took mine to a local non-official iphone repair and they applied thermal paste over the main CPU and the laggy performance issues seem to have reduced a lot, at least pubg and other games are not too laggy as before, but you will loose your warranty. I dont think official apple stores will apply thermal paste for you.