This is handled for example by fake-hwclock package in Debian (also RaspberryPi OS, installed by default) - it saves it in file, and even updates it every hour

This is handled for example by fake-hwclock package in Debian (also RaspberryPi OS, installed by default) - it saves it in file, and even updates it every hour (so you won't teleport more than a hour back in time after unclean reboot). However, it of course does not work when you mount read-only because you don't want your microSD card to fail.