Is there any plan to provide the 3.6 desktop client release for Ubuntu focal (20.04 LTS) through the official PPA?
There is a focal release in the client-beta repository, but not the stable repository.
No, and apparently there will be no more new releases. The reason seems to be the old QT version in Ubuntu 20.04… https://github.com/nextcloud/desktop/pull/4840#issuecomment-1220894350