This is from Lubos Kocman via openSUSE Factory mail list:
We have a “situation” with upgrading of Leap 15.X virtualbox guests to Leap 16.0
since Leap 16.0 doesn’t have Virtualbox guest-tools/kmps needed by
virtualbox guests.
When we were trying to add virtualbox to Leap 16.0 during Beta it
wasn’t building and we really didn’t look into it until now.
We were pleasantly surprised that the situation has changed a bit or
at least it seems to be building successfully against 16.0 in the
devel project as of today.
I do not want to touch the current Leap 16.0 GM build (Build169.2) as
we have release day in two days. And especially in case of such a
complex package, we have to check on the maintenance side first.
Making sure that we can keep Virtualbox building and provide users
with necessary security updates etc.
My advice for virtualbox users is to postpone upgrading to Leap 16.0
until we have official steps. Leap 15.6 will keep getting updates
until 30th April 2026. We’ll for sure have an official solution by
that time. Alternatively, opensuse-migration-tool can give you other
upgrade options than Leap.