PS crashes and causes computer to restart

With these two actions, the problem is gone for me.

Fix 1: Reset Photoshop font cache
Corrupted font cache could cause performance issues for Photoshop. You can try to delete it to allow Photoshop to create a new one. This could solve your crashing issue if it was triggered by a bad font cache. Here’s how:

Close Photoshop and Creative Cloud app.
Press Ctrl and E to open the file explorer, and navigate to
C:\Users\[Your Username]\AppData\Roaming\Adobe\Adobe Photoshop <version>
Delete the CT Font Cache folder. Make sure you empty the Recycle Bin as well.

Fix 2: Test optional or third-party plugins
Problematic plugins could trigger random crashes when you’re using Photoshop. You can first identify if there’s any plug-in causing the problem, then disable it if necessary. Here’s how:

Hold down Shift on your keyboard, and launch Photoshop.
Click Yes to launch Photoshop without loading optional and third-party plug-ins.

Hello, What is the version of iMac that you are using?

If you are on Photoshop 23.3.1, since you reinstalled,

Try disabling the following:

Preferences -> Performance -> (GPU) Advanced Settings ... -> GPU Compositing
Preferences -> Performance -> Multithreaded Compositing

In modern operating systems, applications cannot cause hard restarts. An application can crash or freeze, but not take down the whole system. Photoshop can trigger it, but not cause it.

It's either overheating, or a buggy driver, or failing hardware.

If a reset of pref's doesn't work (and it likely will), the next step is to try the following:

Try logging into another account (you may need to make one), still crashing? 
Try starting up in Safe mode (hold down Shift Key when booting), still crashing? 
You might want to try running a free utility like Onyx: still crashing? 
https://www.titanium-software.fr/en/onyx.html
Also view:
https://www.macworld.com/article/352902/onyx-review-macos.html
https://www.macworld.com/article/224955/how-to-reset-a-macs-nvram-pram-and-smc.html
From Adobe:
https://helpx.adobe.com/photoshop/kb/basic-troubleshooting.html

Try resetting the tools and/or preferences.
To restore preferences quickly using a keyboard shortcut:

Press and hold Alt+Control+Shift (Windows) or Option+Command+Shift (Mac OS) as you start Photoshop. You are prompted to delete the current settings. The new preferences files are created the next time you start Photoshop.
Note: Using the keyboard shortcut, preference files for custom shortcuts, workspaces, and color settings will also be reset to default.

from here:

https://helpx.adobe.com/photoshop/using/preferences.html#restore_preferences