Had some issues with my monitor, too. In the End I got a software solution which fixed my problem.
It´s called "BetterDisplay" and I can set the resolution and the scaling. It helped me a lot after beeing frustrated for quite some time,
as it seemed not possible to set the right resolution for my LG Monitor.
Hope this fixes some of your problems... Just set the correct native Resolution in the menu and from there you can select the right resolution.
SeSam4494
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