Minimum size for /boot?

Is there a hard minimum size for a boot drive?

I’m considering trying to set up Clear on an older NAS (ReadyNas 516) and it has a 240 mb boot drive that’s used by the original OS to load the basics into memory before bringing up the storage array where copies of the rest of the OS lives.

Currently it’s running Ubuntu 22.04, and I can shoehorn an active and backup kernel into /boot by changing the initramfs compression to xz.