Computer freezes after update 2020-002 on High Sierra. How to revert / cancel update?

Since security update 2020-002, I'm having lots of trouble with a macbook pro early 2015 running high sierra

The computer freezes all the time

From what i read, this update causes problems when the graphics are solicited a little more than standard which is my case as I have 24" external monitor always plugged to the computer (hdmi) and i use software such as illustrator and indesign on a daily basis

Is there any way to revert/cancel updates on mac os ?

If it is not possible, my only option would be to get Catalina.
In case something goes wrong with Catalina, i would like to know how to get installers for Mojave and/or High Sierra (i don't 'purchase' mac os versions so i don't have them on my App Store purchased tab)
Is there a direct link to the dmg install files ?

Thanks

Rollback procedure

The only way I found to be able to fight bad OS updates, and to revert an OS update is the following procedure. It is a procedure to have in place before any update and at the same time it is a heavy and pretty good backup policy.

Buy a dedicated disk for this backup and rollback policy, twice the capacity of the disk of the Mac you want to protect.
Make a full bootable backup of your OS with Carbon Copy Cloner (you can try it for free to make your own opinion about the quality of this software).
Once this backup is complete, test it by booting your Mac on it and check everything is OK (your vital applications at least).
Reboot your Mac on its internal disk and make a log file to track which versions of your OS you backud up correctly. For example I use a basic text file I maintain with vi (and rcs):
```
backup disk name        version of the OS saved        date of backup
```
Make the update that App Store proposed you and check everything is OK (your vital applications at least).
If this update is OK, just continue with it: end of the backup procedure.

Else, make a rollback of your previous version saved on your backup disk with Carbon Copy Cloner.

Practical time spent on this procedure

one hour for backup CCC,
half an hour for checking the backup,
one hour for MacOS update,
2 full days for testing the new MacOS version,
one hour for rollback CCC if the new MacOS is ill behaving,

total: 2.5 days (essentially testing a fresh new MacOS version).