This stand is compatible with the magnets on the back of the Samsung Galaxy Tab S9 FE. It uses sixteen 5 mm diameter, 1.5 mm thick magnets.
I designed the base to attach the stand to my keyboard, a Logitech G213, but you can design a custom base to suit your needs.
I then covered it with an inexpensive adhesive cloth that I bought from AliExpress.
I printed this with Rapid PLA, so if you use standard PLA, it is recommended to reduce the print speed slightly, particularly for the stand.