Comment 22 for bug 1988299

> How did you remove the other kernel versions?
I just ran `apt remove` on the relevant kernel packages.
Maybe synaptic has some guardrails to prevent a user from configuring the system to only have a single kernel installed?

> What was your initial initramfs compression setting?
Mine was initially lz4.
This is the default for Ubuntu 20.04 installations I think.
It is actually not a good choice from a space perspective - it achieves a compression ratio even lower than gzip.
Rather, it was chosen because it is very quick, which speeds up boot times quite a bit.
Both lzma and xz should offer substantial reductions in the footprint of installed kernels in /boot, but this comes at the expense of longer boot times.
This is actually moot though, since the upgrade tool for 22.04 overwrites the compression setting (if you let it - I did to no ill effect).