Another alternative approach is to run the nano command with -l (that is a lower case L) so you get line numbers.
nano -l /var/ipfire/qos/bin/makeqosscripts.pl
then scroll down to line number 212 and see what is there.
EDIT:-
So @arne_f took the existing makeqosscripts.pl file and modified two line to make the cake based version run with fq_codel.
If you have not had your makeqosscript.pl file updated because something went wrong during an upgrade then you would still have the previous version of makeqosscripts.pl, which is very different and that portion of the line I suggested would not be found.
Line 212 in that case would be
$qossettings{'CLASS'} = $classline[1];
I recall you having previous problems with missing or outdated files that had to be copied from the IPFire git repo.
If line 212 is from the old version of makeqosscripts.pl then I would suggest doing a fresh install and restore to ensure that all files are correctly brought up to date.
EDIT2:-
The reason I am suggesting a fresh install is that if you donāt have the updated makeqosscripts.pl file then you likely will also not have the following updated files
lib/udev/network-aqm
lib/udev/network-hotplug-bridges
lib/udev/rules.d/99-aqm.rules
srv/web/ipfire/cgi-bin/qos.cgi
which were also changed for the migration from fq_codel to cake.