I got this mb pro new with Catalina preinstalled, it cant be the reason.
What can't be the reason? The amount of RAM? A 15,4 MacBook Pro is a 2019 model that could be ordered with 8 or 16 GB of RAM. I would not have gotten anything less than the maximum of 16 GB. It's too late to change that now as the RAM is not upgradeable after the fact.
As far as the OS, it was originally released with Mojave, but as Apple always does, the same model built later (even though it's still considered a 2019 Mac) has the firmware is updated so it will only boot to the latest OS.
I installed fan control to make it cooler no more quiet and it helps.
Again, this is bad. Very bad. Only Apple's engineers know what the Mac needs to do in order to keep it from overheating, and just generally properly cooled. They designed it top to bottom and know exactly what the thermal specs are. A third party vendor cannot do better than Apple's own engineers.
I don't thing that developers are so stupid to release a product that barely can handle it system.
Every single computer maker does this. They sell computers at the lowest possible price point to make it more enticing to buy. 8 GB of RAM is fine if all you're doing are simple tasks such as word processing and browsing the Internet. When you start throwing in resource intensive apps like Photoshop, you need to take into account how you're going to use this computer and order it accordingly. That means a faster CPU, more RAM, and a larger drive. Especially on a model that cannot be upgraded later.
Back to the issue. Have you (again) created a new user account and tested Photoshop there? We are otherwise both wasting our time by not knowing if the issue is related only to your main user account, or if it's a system wide problem.