Congratulations, you have a Lenovo monitor.
My apologies, you have a Lenovo monitor.
This took me an eternity to figure out with both of my Lenovo ThinkVision T27p monitors a while ago, one would occasionally drop down to 30hz from its 60hz max. I noticed this when connecting one of them over USB-C However, because of how they split the lanes with the hub, if you have too many devices connect either to the monitor or your device, you're shit out of luck and it's Russian Roulette on if you will get 30hz or 60hz, or whatever your theoretical maximum refresh rate is.
Sometimes going into the monitor settings and setting USB Source Selection to USB 2.0 will work, but it's still not a guarantee.
Solution? Return your Lenovo monitor and save yourself the trouble. Don't have the luxury? Switch to a DisplayPort cable. Don't bother with a Thunderbolt dock and connect up your monitor to that, at least not a Dell one. Don't ask me how I know, my wallet is still angry and 300eur lighter. I would be surprised if you get the high refresh rate over USB-C or see above Russian Roulette.
I went through a ton of solutions for this and ended up going the route of a DisplayPort + HDMI KVM switch to my MiniPC and desktop, bearing in mind both of my monitors are 4k60 so I have some cheaper options. Maybe a Level1techs KVM would be good for you? 🤷 Assuming you have DP of course, otherwise good luck 🫡 When I need to hook it up to the work-issued Macbook (fortunately rarely), I just grab a Thunderbolt 4 cable and use the built-in KVM on the monitor. A KVM switch may not be the best option in your case, but I'm just saying what might work the best if your device supports DisplayPort.
Re. 119.88hz, your monitor will typically report multiple modes e.g. 59.499995, or 59.99997, or sometimes literally 60hz. They're all basically the close approximation to the absolute value, sometimes you'll find one works better than another. I've noticed on my Lenovo monitors that the 59.99999hz option provides colors that don't look terrible, whereas the 60hz ones look washed out. Go figure. It shouldn't harm your monitor, but then again all open source software is without warranty so if something happens, that's on you. A monitor shouldn't advertise a mode over EDID if it'll damage the panel.
