A was wondering why the last two Raspbian updates did now't: now I understand why, because a piece in El Reg today says that Debian Buster gets replaced by Bullseye in mid-August with, presumably Raspbian following on shortly. There don't seem the be a lot of gotchas:
- exim becomes 4.94, which won't run without configuration changes
- the lilo bootloader vanishes
- Mailman 2.1 -> Mailman 3
- pyython 2.7 remains but it only there to support a few packages that haven't yet moved to Python 3