27" Thunderbolt Display now turns off after a few minutes at > 75% brightness

I've been using a 27" Thunderbolt display that's worked perfectly for months until just a day ago.

Plugged into an early 2015 13" macbook pro -- if the brightness level is above 60-75%, the screen intermittently "blinks" once or twice, then after a few minutes goes black.

Details:

• The Thunderbolt connector *seems* fine and doesn't get burning hot or anything
• When the screen turns off, the camera, data, ethernet and audio still work
• The only way to resolve is to unplug the display power and thunderbolt from the macbook, and then leave it at 50-75% brightness. When the brightness is lower, I can leave it running the "Aerials" screensaver for very extended periods (hours) with no issue. But put the brightness higher where I need it for work and it will go dark after 10 minutes or so, no matter the content on screen.
• The Thunderbolt display firmware was very outdated the first time this happened; I've since updated the firmware to the latest versions. That didn't change the issue, which is still happening.
• I've done all the PRAM, etc. clear memory steps with no change to the issue.
• I've also been using this display with an HP laptop from work, using Apple's Thunderbolt 2 to 3 adapter. The display never had an issue with this either, now the behavior is the same on Mac OS or Windows.

Is there a straightforward resolution to this issue? I could try to use a Thunderbolt cable with the second video port on the back of the display to my Macbook instead. I don't want to do an expensive repair costing more than the display is worth in 2021 if I can avoid it.

Thanks in advance for the response.