1280 x 720 is going to be too large for some, but also too small for others. There is no "This is the correct resolution".
You can view commonly used resolutions here:
https://screensiz.es/ but keep in mind it isn't just the number of pixels, but also the pixel density and pixels per inch.
If the game is in HTML5, then this would just be a matter of adding some CSS @media rules but I'm not sure how one would detect the screensize automatically in GMS. You may need to programmatically lay out each object based on the viewport/camera instead of absolute values, or make a few different layout versions for the most commonly used resolutions.