If in /etc/zypp/zypp.conf multiversion.kernels = latest,latest-1,running is set and I run purge-kernels will it make adjustments to the grub2 menus or do I also have to run the grub2-mkconfig routine?
No, openSUSE systems are virtually maintenance-free.
Grub2 makes use of a link to the current default kernel and that link is automatically adjusted. Here is part of my /boot directory:
lrwxrwxrwx 1 root root 31 Jul 24 09:10 vmlinuz -> vmlinuz-5.3.18-lp152.84-default -rw-r--r-- 1 root root 9052336 Jul 7 14:03 vmlinuz-5.3.18-lp152.81-default -rw-r--r-- 1 root root 9060528 Jul 21 14:20 vmlinuz-5.3.18-lp152.84-default
No. it does not. At least in default configuration as shipped by openSUSE.
and that link is automatically adjusted.
This link is adjusted during kernel package installation/removal, not by grub2.