How do I get my monitor to run at the correct resolution reliably?
I have the same monitor and running MacOS Catalina 10.15.4. I believe a DVI cable (DVI-to-TB3: https://www.apple.com/shop/product/HLR62ZM/A/moshi-usb-c-to-displayport-cable) would get you higher res options + 75Hz refresh rate. Failing that, try using SwitchResX (https://www.madrau.com/) to expose some other display options.