Hm, I've just found a post that says, in essence, that for most Raspberry Pi systems, Kodi is no longer available:
https://forum.recalbox.com/post/174579

To be honest I'm a bit shocked. Is there anywhere a download for the most recent RPi2 image with Kodi still included? (Oh, and I'd suggest to prominently document such an important breaking change.) My old setup that I wanted to upgrade (on the same hardware which is perfectly fine) dates from 2016. On another RPi2 I have libreelec with a much more modern Kodi. In fact that's the reason I wanted to upgrade in the first place: finally have a less dated UI in Kodi.