How to fix suboptimal mode on samsung monitor?

Question

Monitors

Good afternoon.
I have an asus rog laptop.
Somewhere an old samsung monitor with a resolution of 1280x1024 was lying around, so I want to connect it.
I select this monitor in the display settings and set the resolution to 1280x1024.
A window pops up, where it is written that you need to set the resolution to 1280x1024 and the resolution to 60Hz.
Only I do not quite understand, because I have already set this permission.
And yet, on the sides of this monitor there are black stripes, that is, the picture is not displayed in full screen.
I'll probably buy another monitor later, but for now I want to figure it out.
The laptop monitor has a resolution of 1920x1080, the Samsung has a resolution of 1280x1024.
I set the resolution to 1920x1080 for Samsung and the picture was displayed in full screen. I just don't know how correct this is.
Thanks in advance for your help.

Answer 1

It is possible that the "optimal" should no longer be the resolution, but the frequency, on the laptop it can be 70 Hz