Thanks for the pics!
Unfortunately I have to say that I don’t think the piston, rings and barrel are in very good condition.....
Pic 4 in particular may indicate a piece of the ring missing?
I have seen worse but I suspect the engine is well down on compression which for sure will hinder starting.
Are you happy to take the cylinder off? You’ll need a TX 27 driver.
(All isn’t lost here as piston and barrel kits are available, for a fraction of the Stihl price).
John