Sounds like this is an old install and “admin” was not defined at the time
You may set the setting manually with yunohost app setting peertube admin -v <some_admin_username> with <some_admin_username> being an actual yunohost user on your system
As reported on Matrix, I gathered this feedback for the exact same issue :
ynh_user_get_info --username=$admin --key="mail" won’t work if admin user doesn’t exist.
Is that expected ?
Because in peertube upgrade script it’s used.
And funnier : for one user, yunohost user info admin gives a result. But not ynh_user_get_info --username=$admin --key="mail"
Or maybe you mean the “admin” account in Peertube ?