iMac freezes - mouse, sound still working

Dear all

I do have a very very annoying problem I tried to solve reading several threads for more than a year but the problem still persists.

I have an iMac Mid 2010 which has a following symptom: It freezes, meaning I cannot click or do anything. The mouse is still moving, sound goes on no problem. The system though is not responding at all.

The problem is not easily reproducible but I am now certain that happens once I heavily use safari. It drives me crazy since this is a machine I use at work. I've seen all the posts suggesting change ram, change ssd, install from scratch, clean your imac from 3rd party software that may harm it, I've almost checked all the things but the problem is there. I've also read that the heatsink of the gpu might be dirty blocking the cooling which I will anyway try to clean and install new thermal paste. Also installing from scratch is a pain since I do have many settings on this machine. Restore from time machine is an option though.

Any help is highly needed otherwise this machine becomes useless.

Many thanks in ad