I have a 16GB 2020 Mac mini M1 with the Samsung Odyssey G9 ultra-wide 49″ monitor. I bought this USB-C to DisplayPort cable to get the max resolution of 5120×1440 but I had to jump through a few hoops to get there. Here’s how to do it.
These are the simple steps with macOS Big Sur 11.1:
1. The G9 must be set 60Hz, at least initially (Adaptive Sync also needs to be disabled, but I believe changing to 60Hz does this automatically). So yes, that means you cannot use your monitor at 240Hz. So, boo. I don’t use it for gaming, but rather for productivity/dev so I don’t really care about it. If you do, then keep 240Hz and you’ll have to also live with the reduced 3840×1080 resolution. I’ve been able to get it to work with 120Hz but initially set it to 60Hz.
2. Go to System Preferences > Displays and while holding down the OPTION/ALT key, click “Scaled”.
3. Now select the 5120×1440 resolution. Boom.
This is the way.