Now don’t I feel sheepish!

But seriously, I guess it is possible to use a USB thumb drive on my Mac with only Thunderbolt ports, but I never have and it’s never occurred to me. I suppose I still have one somewhere and maybe a dongle that would let me do it.

which is still a pain in the butt because you have to own, find, backup, and completely wipe a thumb drive to do it. Or you have go to the store because who uses thumb drives anymore?

Macbooks from 2019 have 4 thunderbolts 3 ports and 1 mini jack. And that's all.

If you want to power the device, you do it through a thunderbold. If you want to connect a USB that is not USB C, you have to use adapter and/or USB HUB. So you would have to connect to your USB through adapter/hub, and if for some reason whatever installer wouldn't support this you would be screwed (but I guess most of the time it would be doable, just inconvenient).