Black Screen Then A Shutdown

I'm having a problem with my older backup MBP.

MacBook Pro (Retina, 15-inch, Late 2013)

Processor 2 GHz Quad-Core Intel Core i7

Memory 8 GB 1600 MHz DDR3

Graphics Intel Iris Pro 1536 MB

Serial Number C02MH0HUFD56

It's a great machine and I love it for every day use. I've been running Catalina since it came out and about a month ago I decided to wipe it, entirely and reinstall Catalina. Everything was running fine until a week or so ago when I started getting black screens, then a few seconds later it shuts down.

These unexpected shutdowns are happening more and more frequently - that has me believing some hardware is failing.

I'm not getting any error messages or kernel panic messages, either. No spinning beach ball, no hung or unresponsive apps. It just happens when I'm surfing the web or watching YouTube or pretty much anything.

I did a little research and tried the Reset the System Management Controller method (Shift+Control+Option+Power while it's OFF). No change, I still get black screens and a shutdown.

Next I tried the Reset the PRAM method (Command+Option+P+R keys). Same thing - black screen then a shutdown. No error messages, not hung apps, nothing.

I contacted Apple support via chat and they suggested I create a new test profile, set to administrator. I did that, logged in to the new profile and a few minutes later it shuts down again.

The last thing I installed that might be the culprit is Canon's EOS utility - I use it to shoot tethered from a DSLR. It's not even running at the time of these shutdowns.

What do I do? Is there something to look for in System Information?

I can drop it off at a local Apple Store for service, if I have to, but I'm afraid a repair might be cost prohibitive.

Thanks!