Remote desktop access across a LAN in Windows 11

Question

Short version: We need a freeware VNC solution for a large co-located translation team using Windows 11 on 20+ laptops. And it has to actually work. 

Longer version: 

We have a team of 20+ translators working in 12 languages at the same place at the same time on the same LAN. Before Windows 10, we could easily use UltraVNC to view anybody's screen at any time. This was a huge help for collaborating on a translation together, for giving help, for maintenance, and, with multiple connections to one desktop, for teaching. UltraVNC was a good choice because it was easy to use, very fast and totally free. I had shortcuts on my desktop that got me into all the machines for the six translators I was supporting directly, and I could get on any computer in the workshop if I knew its name. We had the same password to get into all of them and everybody knew the password. None of us had an expectation of privacy because these laptops are for translation only. If somebody wants to work on something personal, we have a couple older laptops available for that. I loved being able to say, "Okay, here's how to do this" without having to look over somebody's shoulder in the tropical heat. 

But we have not been successful in getting UltraVNC to work in Windows 10 or 11. On my last visit to the translation center, which was last October, I was able to make it work with one of the computers but none of the rest. I could not figure out why that one would work. Twice I have spent hours scouring the Internet trying to find the secret sauce to make it work, but have not been unsuccessful. Yesterday was the last time I tried. I would love to get that working again. 

I looked at Windows Remote Desktop, but apparently it requires the remote user to have an account on the machine being accessed. That's a non-starter for us. We can't predict who may need to get into one of our machines remotely. 

I use TeamViewer and had hoped that would work, but it is much more complex than UltraVNC. 

Does anybody have a suggestion for software we could use to do this in Windows 11?

Requirements: 

* Free
* No Internet connection required
* Remote Control or just viewing
* Easy to use, at least after setup
* Works on Windows 11 Pro
* Multiple incoming connections to one computer so multiple people can observe one computer's screen