MacBook Pro with OS Catalina 10.16.7 keeps shutting down and rebooting

my notes suggest the last 17-in MacBook Pro was is a 2011 model, supported by Apple through High Sierra. If you are running a third party hobbyist hack to get to Catalina, that is NOT thought to be a contributor to this issue.

The panic report show suggests your Discrete graphics processor has died. This happened to many of these models as they aged. Replacement parts are hugely expensive and not practical.

there are some work-arounds available, but they come with conditions:

NOT running Chrome, the biggest resource-hog that is not obvious malware AND

not using an external displays AND

willing to disable Processor sleep, and either just sleep the screen or power off when done for the day.

...ask for more details if interested.

removing Chrome and the VPN is great first step.

By far the easiest way to cause poor performance, instability, overheating and crashing is to install ANY third-party speeder-uppers, Cleaners, Optimizers, or Virus scanners, Bit Torrent, or a VPN that you installed yourself. They are relentless in scanning your files, non-stop, looking for virus-like patterns in Everything, or looking for files that have changed. When completed, they do it all again.

Install Cody Kreiger's Open-Source gfxcardstatus, (https://gfx.io) and set it to "i" (integrated graphics only). It will allow your MBP to run on integrated graphics only, bypassing the discrete GPU which has the issues. This may allow your MBP to run normally, although it will have reduced graphics performance when performing demanding graphics tasks. The alternative is replacing the logic board, which is not cost effective on a machine that old, unless gfx does not resolve the issue and you really want to keep this MBP.

if this does not make the issues FAR less, the more extreme work-arounds require a bit more focus, but no high level skills.