I have a the ROG SWIFT PG278Q monitor, which notably only has a DisplayPort connector, no HDMI. I tried connecting it via a DisplayPort-DisplayPort cable to the DisplayPort expansion card, but the monitor was not recognized (
xrandr didn’t show any of the DP-* as connected).
After some troubleshooting I concluded that the DisplayPort expansion card must be the problem, since both the laptop and the monitor worked independently, but the connection between them isn’t. So to fix this, I ordered a DisplayPort-USB-C cable to connect the monitor directly to the laptop (with a USB-C expansion card), and to my luck, that indeed worked like a charm!
Note that in order for the 2560x1440 resolution to work for this particular monitor, I had to follow the instructions in this blogpost:
So while I now know that the problem was with the DisplayPort expansion card, I’m not sure if it’s just my expansion card that’s faulty, or if it’s a generic problem with them. I couldn’t find any others with the same problem, so I’m guessing it’s probably the former.
This is just a PSA for others maybe running into the same issue.