I used citrix workspace on endeavour OS (KDE), multi monitors (full screen across multiple monitors or one screen only), without problems.

I'm remoting into my work machine with RDP in a similar way, also using multiple (local) screens. I happen to be on CachyOS (Arch), but I would assume this works on any distro.

I just call xfreerdp3 directly with the appropriate command line options to span my local monitors which I want to use. I only use 2 of the 3 I have, as the 3rd remains for my local stuff.

Zero issues. Just works once setup.

A lot of people keep suggesting Remmina, but I couldn't get that to work even slightly. Let alone with fine grained control over monitors.

Probably doesn't need to be said, but make sure doing this won't get you in trouble at work. Most enterprises would likely consider this a security issue, and most larger ones actively monitor what software is installed on workstations.
Edit: I see now you say this is commonplace where you work.

Remmina