No. Librem Tunnel is a VPN service, like those other ones. It’s part of the “Librem One” bundled subscription that includes:
Librem Mail
Librem Chat
Librem Social
Librem Tunnel
For comparison, think ProtonMail + ProtonVPN, for example.
I would say first try to install whatever client the VPN service provides for Linux Debian/Ubuntu. If the client doesn’t work, or if they don’t provide one for Linux, you should still be able to download their OpenVPN configuration files, then use the Advanced Network Connections app as I described above.
I think we have to make a distinction here: Most any VPN service should work on Linux, but not all of them provide client software for Linux, what some people might call an “app.” A client does nothing special; it just presents the controls to you in a nice clickable package. Really, it’s the code underneath that does the magic and makes the secure connection over the internet. The protocols, e.g. OpenVPN, IPsec, etc., are the same, irrespective of your OS.
EDIT: This flatpak should work, too: eOVPN
Think of it as a generic OpenVPN client, for when your provider doesn’t make one available for Linux.