It's a cautionary accidental because of the E natural in the previous measure. All of the editions that I have, Schenker, Schnabel, Arrau, von Buelow, Craxton-Tovey, Casella, old Peters etc. include it and some position it before the trill as was Beethoven's practice.
Most editions correct the enharmonics (Scbenker), but Schnabel doesn't. I'll keep it as in the manuscript and first edition in my edition because it's typical of Beethoven trying to keep the chordal notation user-friendly for the players who might be uncomfortable in a key that was not so common at that time.
The trill and the enharmonics are all notated exactly the same way in the recapitulation transposed to the tonic key, so it is definitely intentional and not a slip of the pen.
Here is another one from the first edition of op. 106:
![op 106 trill.jpeg](./download/file.php?id=3235&sid=feecc30d2429009e3d657270c195acf5)
- op 106 trill.jpeg (61.67 KiB) Viewed 12019 times
M1 Mac mini (OS 12.4), Dorico, Finale 25.5, GPO 4, Affinity Publisher 2, SmartScore 64 Pro, JW Plug-ins, TG Tools, Keyboard maestro
http://www.cantilenapress.com