Telegram on phone shows that my desktop session is on “Xen” rather than stating its fedora like other services do (google etc.).
Makes me wonder what/who else can see this.
Are there any ways to prevent or spoof OS fingerprint on Qubes?
If you run lscpu in an appvm you can see you are running xen, any application will have access to the same information.
Hypervisor vendor: Xen
Virtualization type: full
I’m not an expert but i think it’s just impossible. Software will always detect by a way or another your current distro. Telegram detect you’re using Xen because there is Qubes files inside your appvm and you can’t hide that to the software. (someone will correct me if i’m wrong) Even if you find a way to spoof Qubes how can you explain the fact there is Qubes files inside your system 
Correct me if i’m wrong but if Telegram can know you’re using Xen imagine what Google the biggest tracker / spyware compagnies know about you… They proably know you’re using Xen and Qubes too.
Preventing applications from seeing they are running in a qube is possible but will take some time+attention to implement by someone who knows what they are doing. Unfortunately those who have some of such relevant skills (myself included) are usually booked solid.