Upgraded to ynh 11 without (many) issues, but I have your same issue with gcc-8-basepackage.
Following you advice @Aleks
root@ynh:~# apt-mark showhold
root@ynh:~# apt-mark unhold gcc-8-base
gcc-8-base was already not hold.
root@ynh:~# apt upgrade gcc-8-base
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
libgcc1 : Depends: gcc-8-base (= 8.3.0-6+rpi1) but 8.4.0-7+rpi1 is to be installed
E: Broken packages
most important apps in my server work fine (I’ve just to repair Calibreweb) so so far it is not a big issue.