Joy of joys...
=== Error: Transaction test error: installing package kernel-core-6.8.8-100.fc38.x86_64 needs 13MB more space on the /boot filesystem installing package grub2-efi-x64-1:2.06-118.fc38.x86_64 needs 20MB more space on the /boot filesystem ===
Today Fedora decided that 400MB of /boot space wasn't enough to hold 3 kernel versions, a rescue, and grub. And that's not the easiest fix in the world...
My longest-continuously-upgraded systems were expanded a decade+ ago from whatever (100? 200? MB) to 400MB, which Fedora recommended at the time. Luckily some later ones I set to 500MB which should be ok for a few more years. The new Fedora standard seems to be 1GB.
Easiest fix for now is to edit dnf.conf to change installonly_limit to 2 rather than 3. However, that isn't ideal as there have been times I had to go back to that 3rd-oldest kernel. I guess another option is to disable the rescue kernel, which is always so old I don't even know if it will even work. In fact, I just talked myself into the latter option until the next disk upgrade when I can do some gparted partying.
Then the question will be: how long will 1GB be enough space?