I found a fortress mid-game that seemed nearly unbreakable

But apparently, I could have opened it up at some point?

Also why is 19... f6 bad? (I will block you if you answer it Ben Finegold way) (jk)

20. Bxf6 xf6 21. Qg6+ and White can force a draw if they want.

@dnowmects Yes but the eval is +3. Why?