I ran 'apt-get update && apt-get upgrade' on a fresh MoodleBox v4.5.1 and was bombarded by pages and pages of "rpikernelhack" messages and about the same number of warnings on overlay changes. It finished ultimately and to my surprise, I am served with a 'Linux moodlebox 6.1.21-v8+ #1642 SMP PREEMPT Mon Apr 3 17:24:16 BST 2023 aarch64 GNU/Linux'. Not that I have something against kernel 6.1, but I find it odd that a distribution jumps to the next generation of Linux kernel just as part of its normal system upgrade - not to mention the scary messages.
Then I made a 2023-02-21-raspios-bullseye-arm64-lite. It behaves identically. So this comes from upstream. Now reading the forums I find reports going back to two yeas and reassuring that it is normal. Still, I think, if the next MB would have this step already done, it'll save some raised eye-brows.