Download OBS Studio https://obsproject.com/download
Install it
Run OBS

File, Settings

Tab: Video
Change Base and Output to be the same resolution (1920×1080 probably)

Tab: Output
Encoder: Hardware (Anything)
Recording Format: mp4

ok, close out of settings

Sources [+] (at the bottom)
Display Capture
[ok] [ok]

Check your video looks right in the video area (Should be showing your desktop)
You can click in there and resize, but if you need to do that you probably didn’t get the video resolution correct before.

Ready!

Hit [Start Recording] to record.

In the future you should just be able to start OBS, the display should already be in the video pane, hit [Start Recording]