Pixelated font on Catalina with external monitor

I have been enjoying my DELL U2713HM with 2560x1440 for quite some time now. Extremely crisp and beautiful display. Recently I replaced my rMBP 15" mid 2015 running Mojave by a new MBP 16" 2019 with TouchBar running Catalina. Now fonts on the DELL look awful. Everything is kind of grainy and over sharpened, no matter whether font smoothing is on or off. All the settings have been migrated from Mojave to Catalina, the monitor settings have not been changed.

I started playing with the monitor's sharpening settings but things got worse, either over crisp or too blurry.

It seems that Catalina does not properly recognize the monitor or has changed something drastically in font rendering. How can I get back my perfect picture?

Due to USB-C/TB-3 on the new computer I had to connect the monitor's display port through a Thunderbolt Dock (OWC). Could this be a cause? How should I connect the monitor as it does not have a TB port.

Thanks for any help.