Dell WD19TB with MacBook Pro 14 M1 Pro

Hello!

I own a Dell WD19TB for more than a year and I mostly used it for my companies notebook (Dell 5520) which works fine. My dual monitor setup is monitor 1 (27" 2560x1440@144hz ) and monitor 2 (27" 3840x2160@60hz ), both from LG.

Both of these are connected to my WD19TB. Monitor 1 is connected via HDMI to USB-C (to Thunderbolt Port on Dock) and monitor 2 is connected via DisplayPort to DisplayPort on dock (the left one).

I refered to the instruction from Dell for using an Apple USB-C (Thunderbolt) host due to lack of MST (Multi Stream Transport) under macOS. 

https://www.dell.com/support/kbdoc/de-de/000124312/dell-thunderbolt-dockingstation-wd19tb-und-apple-usb-c-hosts

Monitor 2 (4K) works pretty well, but monitor 1 (WQHD) just scales down to 1920x1080, mostly even to 1280x800.

macOS display settings

Any recommendations or tips on how to get this working? I really don't want to use two USB-C cables... plugging them in all the time is not that nice and lowers the reliability of the USB-C/HDMI port... 

Oh, one more thing to mention: when I plug monitor 1 to the HDMI port of the MacBook, it works pretty well. Even at 100hz (60hz is fine for me on macOS, I only need 144hz on Windows for gaming)