The "Add to Home Screen" button is not appearing on my iPhone XR

When you tap on the Share/Action icon at the bottom of the screen, did you try swiping from right to left to see if it appears further to the right?

It should be on second raw (try to slide it to the left), or it could be added tapping on the 3 points, at right end of the second raw.

Giulio

Did you try force closing Safari and restarting your phone?

Excellent, glad to hear that yo got it sorted out.