It seems that you may be conflating phrasing slurs with ties.
Ties and slurs are notated similarly, but the context determines what is intended. Ties in this style will only ever connect two of the exact same notes, and there will not be any intervening pitches; instead, the tie's purpose is to lengthen the duration of a pitch you are currently playing. This happens in the first half of m. 22; on beat 2, the F-doublesharp is tied into beat 3!
A phrasing slur, however, will often connect multiple different pitches, including perhaps multiple instances of a single pitch. That is what is happening at the end of m. 22. During beats 3 and 4, those two F-doublesharps are not tied together, but are rather part of a larger phrasing slur. As such, you will articulate both of those F-doublesharps.
And the same applies to the G♯s at the end of m. 23 and the A♯s at the end of m. 24.
In the instance that you would want to hold the F-doublesharp for the duration of this slur, you would need to use separate voices, like so:
(This looks a little ugly, but mainly that's because it's a manufactured example. Beethoven would have written this differently had he wanted the F-doublesharp held.)