OP is using an LG Ultragear gaming monitor which support the preferred resolution reported in the EDID "3440x1440 143.923 Hz", so this definitely has something to do with linux doing something different than windows/macos.
We don't know that. OP never states what monitor he has, and "LG Ultragear" isn't a model. There's a range of models under that moniker, and if you look at LG's website, the max refresh tops out at 240Hz on some of them … and at 120 Hz on others.
