The world update I did yesterday on 3 different machines resulted in non-working ethernet and USB on all of them.
1st machine: i7-4770, running kernel debian-sources-lts (4.19.194_p3, not updated yesterday)
2nd machine Ryzen 7 4700G APU with built-in graphics running debian-sources (updated yesterday)
3rd machine: Ryzen 7 5900X with Radeon HD7970 video, running also debian-sources, also kernel updated yesterday

World update was done in the usual manner,
ego sync
emerge -avuDN @world
emerge -av @module-rebuild
emerge -av --depclean

After reboot, neither of the machines has ethernet connectivity at all, and the first 2 don't have working USB ports either. It looks that in dmesg, there is no more activity after disk detection, i.e. none of the other hardware gets detected.

I don't know what caused this, off the top of my head the only possible culprit may be linux-firmware but I can't vouch on that.