This reminds me of my tragicomic experience trying to install a calculator on my work iPad.
First one I tried had ads.
Second one required making an account.
Third one had some features reserved for the paid version (e.g. factorial).
Then more adware and other crap.
After 20 minutes I gave up and used pen and paper.
Same with PDF reader. A simple one that just let you read and annotate is something I guess no one is asking for. Everything has a premium plan that is a subscription.
This kind of UX is why I ended up installing a bunch of the official geogebra apps on an ipad in the past. Although, almost any calculation you'd want to do on a calculator can be done inside of spotlight search.