either download the official APK from f-droid.org or use the NeoStore app which is a better client imho. from there its some simple setup and basically works like the play store.

~150 total and 67 on f-droid/neo store so like half is FOSS

TPB isnt the best source for media and it can’t really hold up to its past glory anymore - you could give other sites like 1337x.to a try

1337x.to is pretty good

Lineage is by far the most popular custom ROM and it has about 3.2 million active devices. Which is about nothing in comparison to 1.22 billion smartphones sold alone in 2022. Barely anyone uses third party ROMs.