Template manager fails to fetch template list after in place upgrade to 4.2

[Flex]

Hello,

when opening/refreshing the template list in the Qubes Template Manager
it shows: ERROR: qrexec call 'qubes.TemplateSearch' failed: unexpected
data format.
The same error is displayed when trying to install templates in the
terminal.

Does anyone know how to solve this issue?
(might be similar to https://github.com/QubesOS/qubes-issues/issues/8303)

Could it be the case that the upgrade script was not fully completed
without showing this explicitly as an error in the end? Would there be
any harm done in repeating the last steps of the upgrade script as
stated below?

sudo qubes-dist-upgrade --all-post-reboot
or only:
sudo qubes-dist-upgrade --convert-policy, -p

Many thanks,
flex