Just putting this up here if someone wonders what is going on.
The rear USB-C ports stopped accepting input from an attached old Apple USB keyboard after updating from 27.2 to 27.2.1, but the front ports still works (tested all ports now and the general description is correct).
Interesting. I assume you already tried a power-cycle?
The rear ports are USB4/Thunderbolt ports, while the front ports are USB3-only. So they (probably) use different device drivers.
Definitely report this to Apple via their feedback page. Be as specific as you can, including the model number of that keyboard. You won’t hear back from them, but hopefully someone will read it and fix the bug in the next update.
Well, yes, it is most likely because of the difference between the drivers for these ports and that one or both of them have been updated. Yes, already reported to Apple, but the value of that is not too clear although they lately got back to me for the first time since they started using the Feedback Assistant instead of the old Bug reporter page, where they almost always got back to you. (When they recently got back to me they came across as if they did not know they had already just fixed the problem I reported … hmm, but could always spam them a little and maybe something trickles through. Also the feedback assistant itself has bugs … as sort of to prove where Apple stands on solving feedback sent to them, but think they just solved the most hopeless one where it changes to iOS after starting with macOS.)
Mentioning as it may also affect other USB 2.0 devices and could come as surprise to some relying on old attached devices and maybe controlling a Mac mini remotely.