How to make small item into MagSafe accessory

(Previously posted by Karigram on Feb 7, 2022 with no answers; so reposting with some edits below):

I have a MagSafe phone and case. I want to MagSafe-ly attach a Thinoptics reading glasses case phone accessory (not available in MagSafe) magnetically to my MagSafe phone case. (Attached readers case to previous phone case with adhesive. Obviously don’t want to do that on new MagSafe case.) Not sure if I need a MagSafe metal sheet or a magnetic sheet to attach with adhesive to back of Thinoptics readers case? Is there something available on the market I can safely place on the back of my Thinoptics readers case to keep them close at hand on the back of my iPhone MagSafe case?

Magnets can attract certain metals such as iron/steel, or other magnets' opposite poles (positive to negative pole will attract) but will repel another magnet's same pole (positive to positive or negative to negative poles will repel).

Examples of each from Amazon below, (or if you have used a different item that has worked for this purpose, please post a link) :

This item will turn a non-MagSafe phone case into a Mag-Safe phone case, but if I put them on the glasses case, will they repel my MagSafe case?

https://www.amazon.com/dp/B09PG57NXN?ref_=pe_623860_70668670_dpLink&th=1

Or do I need a ring that is not itself magnetic but will be attracted to a magnet? Such as this:

https://www.amazon.com/WYNK-Magnetic-Wireless-Charger-2-32IN/dp/B077XQLVRY/ref=sr_1_9?th=1