Official document: https://www.jetbrains.com/help/idea/settings-tools-settings-repository.html
With Personal Access Token (PAT), as far as I tried, it is impossible to push changes to private repos. Therefore it is impossible to use https:// git url as sync rpeo.
With firstname.lastname@example.org URL, jgit (jsch) emits authorization errors on sync even if the SSH pub key is added to your Github account. This is because jgsch does not support OpenSSH format ssh private keys.