How long can your Mac run hot until it is not safer anymore?

Your computer will shut down before it gets "too" hot.

Keep your Mac notebook within acceptable operating temperatures - Apple Support

The bottom line? Mac notebooks are not really designed to be "gaming" rigs. You should consider getting something from Alien Computers for that ... or getting an eGPU.

Regardless, when operating at high temperatures, your Mac's electronic components will "wear down" faster. However, as BobTheFisherman has pointed out, your Mac has a built-in "safety mechanism" to protect it when a certain temperature level is exceeded.

I'm more than a little amused when people ask if it is safe to play games on a Mac. No one asks if it is safe to edit video or batch apply filters to a folder of photos. Both tasks are likely to run the computer just as hot and for a long period of time.

Not sure about the 2019 models but the thermal shutdown point in older MBPs was about 100°C