Hi Nicolas,

You should create an A record for the main domain with our IP's and then a CNAME as the
sub domain for branch mapping on this custom domain.
Our IP's for the A records are,
34.236.22.110 and 3.217.205.239.

This will allow you to map you main domain and have all branches as a sub domain via CNAME records.

Please note the following article regarding SSL.
How to set up SSL for your custom domains

I have checked using the TalentLMS branch domain fippi-leanthink.talentlms.com and I am able to use the full screen
option there without any issue, so this is why I believe the issue is the mapping.

Kind regards
Jack