Does M1 Mac support ultra-wide displays?

I'm looking to buy a new M1 Mac Mini but I'm concerned about the potential issues with its support for ultra-wide displays.

I know that in a recent version of Mac OS some fixes have been made and now it supports full resolution for ultra-wide displays, in particular 3440x1440.

My current monitor is 38" with 3840x1600 resolution. Is that resolution supported by M1 Macs via HDMI? (when using a high speed cable, of course)

And, most importantly, is it possible to scale up the UI without sacrificing the pixel density? In Windows or Linux it can done by setting the UI scale to 125%.

I have the M1 Mac Mini and it works with the Dell U4021QW 5120x2160@60hz. The only downside is the brightness keyboard controls do not work and any utility apps that use DDC/CI do not work because Apple didn't implement DDC/CI in their Apple Silicon ARM kernel. Perhaps because of an Intel function found in Intel processors. So other than only being able to adjust the brightness on the monitor itself it's a very nice monitor.

The Dell monitor has USB-C Thunderbolt 4 input and that's how I have it connected. It scales nicely. Hold Option key when clicking Scaled to see the list of optional scaling.

The stated supported screen resolution on the M1 Mini is:

Up to 4096 by 2160 pixels at 60Hz (HDMI) Up to 6016 by 3384 pixels at 60 Hz (Thunderbolt).

Retina Scaling doesn't change the actual pixel density. Your monitor will still display 3840x1600 pixels, but everything will be 2x bigger than standard. Or 1.25x, or whatever scaling you choose.