I have this constant problem with Ubuntu boot partition size, however I can't resize the other partition because it's an LVM encrypted partition.
Resize the ext4 boot partition to give some 200-300MB to the fat32 boot partition.
Reinstall all the system with Timeshift to recover all my data and have a bigger boot.
Move boot in another hard drive.
My actual hard drive:
I've been stuck with this problem for months. I was able to upgrade to Ubuntu 22.04 after deleting all the kernels, but now I can't even perform an update/upgrade because of insufficient disk space.
