Could you elaborate this and provide some references, please?
I think every new Raspberry Pi OS (was Raspbian once) mentions this in their release notes. For instance, for the Buster release:
We do not recommend upgrading an existing Stretch (or earlier) system to Buster – we can’t know what changes everyone has made to their system, and so have no idea what may break when you move to Buster. However, we have tested the following procedure for upgrading, and it works on a clean version of the last Stretch image we released. That does not guarantee it will work on your system, and we cannot provide support (or be held responsible) for any problems that arise if you try it.
Ah, thank you for the link!
In my opinion, they are making it a little bit easy on themselves here, but I guess, that they do not want to let the (normal) user go through the entire partitioning resizing process of /boot/ here.
They also increased the partition of their official images, due to the large kernel files of Debian Buster:$ fdisk --list * | grep "Device\|img1" | column -t Device Boot Start End Sectors Size Id Type 2020-12-02-raspios-buster-armhf-full.img1 8192 532479 524288 256M c W95 FAT32 (LBA) Device Boot Start End Sectors Size Id Type 2020-12-02-raspios-buster-armhf.img1 8192 532479 524288 256M c W95 FAT32 (LBA) Device Boot Start End Sectors Size Id Type 2020-12-02-raspios-buster-armhf-lite.img1 8192 532479 524288 256M c W95 FAT32 (LBA) (retropie) $ df --human-readable /boot Filesystem Size Used Avail Use% Mounted on /dev/mmcblk0p1 512M 47M 466M 10% /boot