Hi Alexander_659,
Thank you for the response.
Regarding with your question on the offered screen resolution, yes, you got it correctly. However, you mentioned that you are connecting the external monitor through USB-C to HDMI, checking the external monitor specs (Samsung 57" Odyssey Neo G9), it shows that it also has a DisplayPort available. Please try to connect the monitor to the Surface through DisplayPort to USB-C then see how it goes. DisplayPort will allow you to use the highest supported resolution and refresh rate with your Surface.
Let me know how it goes.
Kind regards,
Marrion