I’m a semi-pro jazz piano player (meaning, I’m good enough to get paying gigs, but I don’t do it for a living). I’ve definitely performed solo piano many times. I know it’s not quite the same as guitar but hopefully it’s still insightful.

You use the term “sight reading”, but I would never perform a piece I’d never seen or heard before solo. If I’m playing solo, I get to pick what I play, so why would I play something I hadn’t rehearsed?

Now, that doesn’t mean that I might not pull out a piece I’d never performed solo before. There are lots of jazz standards that I’ve played many times in a trio or quartet, so I’ve heard and played the song many times before, but I never had to play the melody, chords, and bass line solo. I’m a strong enough player that I’d be comfortable coming up with a solo arrangement on the spot - but it’d depend on the piece, of course.

I’d definitely use a lead sheet for that, but I’m not sure I’d call it “sight reading”, because I know the song. The lead sheet is there to remind me of the exact notes, rhythm, and chords, so that I’m not relying 100% on memory. It takes all of the pressure out of trying to remember exactly what chord to use - but to be honest, if it’s a piece I’m going to play solo, I’ve probably played it enough times that I could get it 95% correct just from memory and by ear.

When playing in a group, that’s completely different. I’ll sight read new pieces all the time. If someone else knows the melody and all I need to do is play the chords, that’s super easy. By the time they’ve finished the melody and played the first solo, I’ve got the feel for the piece well enough that I can do an improvised solo while sightreading the chord changes.

I have sight-read the melody before, in a group setting - but that’s far more terrifying and less forgiving. I’ll only do that if it’s clearly a very straightforward or easy piece, like a ballad or showtune, with no surprises. If I do that I’ll deliberately take liberties and add flourishes so that anybody listening who knows the song doesn’t think I’m playing it incorrectly. Trying to play the notes on the page strictly means that if I make a single mistake, everyone will hear it. But if I pretend I’ve heard the piece a hundred times and have fun with it, then if I play a “wrong” note (but one that fits with the chord), it won’t sound like I don’t know the piece, it will sound like I’m just doing it a different way.

I hope that helps!

As a jazz beginner, I’d say one of the best things you could be doing right now would be to attend jam sessions. If you can find a good beginner-friendly jam session you should be able to play along with more experienced players and have a chance to occasionally play a solo or melody.