For reason I cannot figure out, the code for slowroll will not install with kernel-default. It will only install with kernel-longterm. I think it is hard coded into OBS.
for those wanting to get it to work.
as root
zypper in kernel-longterm virtualbox-kmp-longterm
zypper rm kernel-default virtualbox-kmp-default
zypper al kernel-default virtualbox-kmp-default
zypper in virtualbox-guest-tools
reboot
now 7.0.20 is in slowroll.