Can 8.x extra repositories be used with RL 9..x?

Newbie question of the day (I presume the answer is something like “you really shouldn’t due to dependencies and shet”, but still:)

For instance Skype and Forticlient VPN offer RHEL repositories for RHEL 8 and 7 but apparently not for 9, at least not yet.

Can I use such additional application-specific repositories in Rocky Linux 9, or is it a no-no? I’d naturally prefer for those two applications to get updated automatically through their repositories, and not me having to manually re-install them every time I want a new version.

Is the fact that they don’t offer repositories for RHEL 9 a sign that they don’t care (anymore), or does it just take so much time to offer a new repository?

It is not recommended to use packages built for another release. Even if it does install, you may uncover issues that you won’t be able to resolve. Some third parties unfortunately take their time presenting a new repository for a new version of a distribution. From my experience, Skype has always taken a long time to get new repositories.

You may be able to get Skype in a flatpak for the time being. But for fortinet, you may need to continue waiting.

You can install Skype as a Flatpak.

Ok, I guess I could use the flatpak version of Skype, if it gets updated semi-automatically.

For the forticlient, I guess I can live with using openfortivpn, which seems to be available ok. I am using it successfully on two other Linux (Mint) laptops, but figured I’d like to try the official client this time, but no biggie.

The third app that I need is Remmina (or a similar RDP-capable app), but it seems to be available with dnf install, as well as as a flatpak.

It is unclear to me, do the flatpak versions get updated, and at what point? Do they get updated whenever I run “sudo dnf upgrade”, or do they get updated through some other process?

EDIT: Well, a quick google suggests it is merely “flatpak update”. I guess I need to remember to run that from time to time as well. I already have e.g. the Steam gaming client installed as a flatpak, works fine.