There are 30 including enharmonics without going into double sharps/flats: B, F#, and C# major can be written as Cb, Gb, and Db major, and G#, D#, and A# minor can be written as Ab, Eb, or Bb minor. There are a couple caveats just due to trends though: B major and Db major are overwhelmingly the versions used because there's 5 accidentals in the key signature compared to the 7 of Cb and C# (although they do still pop up from time to time), and for minor keys, where the major 6 and 7 are also very commonly found, Ab, Eb, and Bb minor are much more common since raising the 6 and 7 of G#, D#, and A# minor leads to frequently seeing at least one double sharp. Double sharps and flats aren't hard to read, it's just that if the same ones are going to be repeated throughout a piece or if due to a modulation or tonicization the music becomes mostly double accidentals, the best practice is to just rewrite the whole piece or affected passages in a way that minimizes them while still being "correct" (i.e., if writing a piece in G# minor you wouldn't just change all occurences of F double sharps to G naturals, it's better to just rewrite the whole thing in Ab minor).
