It'll work fine and you'll end up with lots of timeline real estate. Here's what PD looks like on a 5K (5120x2160) 21:9 monitor:



With that said, I prefer to run PD on my second (4K) monitor because it's sufficiently large and that frees up my 5K monitor for everything else.

Thanks for showing Optodata. 5K looks great but will be also (a bit) too expensive (I just spend 2300 Euro for a i910900k workstation). As you say that you prefer also a 4k, I think I will go for a 28" 4k monitor (16:9).
Just one more question, is it possible on your 21:9 5k monitor to split up the PD view like on a two monitor setup, means full preview on the right side of the monitor and timeline on the left side? Recware: DJI Osmo Pocket, GoproHero7Black, PanasonicFZ300/HCX909, Sony PXW-X160.
Software: Vegaspro365+Vegasaur/PowerDirector365
Hardware: i910900k,32GB,GTX2080s, 1920x1200 display
Playware: Samsung Qled QE65Q6FN, Philips 55PFL7108

Yes. You can undock the preview window and resize it and the timeline section any way you like:

Also the reason I got a 5K 21:9 was because I wanted to be able to see 4K videos at their full resolution so the monitor(s) need(s) to be 2160 pixels high.

With a 21:9 1440px monitor, you'll always see a reduced 4K view while a standard 4K 16:9 2160px monitor will give you the full experience and that might be better overall.

Thanks for showing me the possible screen combinations.
I record in 4k but still produce in 2k. On my 65" UHDTV at normal viewing distance, I don't see a difference between the original 4k recording and the downscaled 2k version of it. The downscaled 2k version just looks great despite the less resolution and a bitrate and file size far less then the original recording. So I don't directly see a need to judge the full 4k resolution on my editing monitor. So I'm still considering between a 3840x2160 monitor or a 3440x1440 monitor.

By the way, it seems you have more experience with PD than with cutting a tree.... Recware: DJI Osmo Pocket, GoproHero7Black, PanasonicFZ300/HCX909, Sony PXW-X160.
Software: Vegaspro365+Vegasaur/PowerDirector365
Hardware: i910900k,32GB,GTX2080s, 1920x1200 display
Playware: Samsung Qled QE65Q6FN, Philips 55PFL7108

Yeah. Unfortunately that was a family member's house after a tremendous windstorm we had last month. They're in the mountains and winds reached over 80mph/130kph and the top 40+ feet/12m of 2 different redwood trees broke off and destroyed their living room

I have 3 short videos (including the one I used for these screenshots) in this playlist if you're interested.

I hope for your family member that he wasn"t watching an optodata video production in his living room when this happened. This is a real huge damage to the house and makes it uninhabitable. Hopefully he's also a good insurrance. Recware: DJI Osmo Pocket, GoproHero7Black, PanasonicFZ300/HCX909, Sony PXW-X160.
Software: Vegaspro365+Vegasaur/PowerDirector365
Hardware: i910900k,32GB,GTX2080s, 1920x1200 display
Playware: Samsung Qled QE65Q6FN, Philips 55PFL7108