The above solutions were too complex for a lo-code guy like me.
I wanted to make one field read-only on the Edit page.
I selected the field, and under Advanced in the LH pane, I unlocked it.
I then clicked on Display mode in the Properties.

This changed to look like this

In the Formula bar at the top of the screen I saw

I don't know what to put there, so I deleted it completely.
The original Display mode has how lost the Fx symbol, and is now a dropdown with three choices, from which I selected View

I tested and it worked