I can’t reproduce. Could it be that your firewall blocks for example ghcr.io? See NS7 NS8 migration disaster - #24 by mrmarkuz
Maybe it’s a faulty software repository? You could try to disable all repos except the default one and NethForge and try again.
Yes, it’s possible to update the apps on CLI.
Example for updating the mail app:
api-cli run update-module --data '{"module_url":"ghcr.io/nethserver/mail:1.7.3","instances":["mail1"]}'