Bug#948257: depmod: ERROR: ../libkmod/libkmod.c:515 lookup_builtin_file() could not open builtin file '/var/tmp/mkinitramfs_XXXXXXX/lib/modules/5.4.0-1-amd64/modules.builtin.bin'

[debian]

so, what's to be done now? Marco d'Itri says that this error is 
pointless, Bjørn says that this is normal and this behaviour is expected 
sometimes (kmod looking for nonexistent stuff)

is it just a harmless error "spam"? update the system as usual and just 
ignore the error "waterfall" in the console? use the patch (the edited 
line in /usr/sbin/mkinitramfs) and then update?