Once I log in to my Mac will it will restart?

To add to previous suggestion

Part 1 of 2

Suggest the User start with Points 1 to 4 and then Test

Still having issues, move onto Steps 5 and 6 and Test Again

Still no resolve - move onto Step 7 and follow instructions therein 

1 - Restart in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal.

2 - Safe Mode will also eliminate Third Party Software, extensions and drivers from loading. It will only load the Minimum amount of Core Apple Processes to allow the the computer to function at a reduced Level of Performance 

3 - Does the issue present in this mode ?

4 - Sometimes a Safe Boot followed by a Normal Boot will just put things right.

5 - If not - there could be something in the main User Account playing up. To further isolate this - Set up users, guests, and groups on Mac. Then log out of the Main User account and log into the dummy account and test again if the issue persists.

6 - If the issue is present in the dummy account - then, this appears to be a System Wide issue on the computer.

7 - Download the Application Etrecheck directly from the Developer.

This is a Diagnostic Tool that makes no changes to the computer.

It makes a coherent and readable inventory of both the Hardware and Software used on the computer 

The application is free or paid from added features. 

The Report will Not Reveal Any Personal Information. 

Post back the Full Report - copy and paste - >>>> using the Additional Text Icon ( 3rd Icon to last ) <<<<

Part 2 of 2

Any Third Party Applications that will interfere with the normal operation of the OS,  is an invitation for disaster. 

Certain Applications maybe available on the Apple Apps Store - this only means the Developer is prepared to pay Apple a portion on each sale. What the Application may do to the computer is up to the User to check this out before purchase

Any of the below listed Applications would show up the Etrecheck Report

1 - Disk Cleaner 

2 - Third Party Security Software 

Any of the above should be removed as per Developers Instructions 

Boot macOS Safe Mode: hhttps://support.apple.com/guide/mac-help/start-up-your-mac-in-safe-mode-mh21245/mac

If that works, then it is some 3rd party software, or something you have in your account's Startup Items.

Have you tried Safe mode? If so, then I guess you are hosed.

If you have not tried Safe mode, then please try it, as it does not load any 3rd party software, and it uses more conservative drivers, and it clears various kernel caches.

Have the computer evaluated by the Professionals who have the smarts and equipment to test the computer

Apple Repair and Repair Status Check - Official Apple Support