I love this solo, one of the earliest things I have transcribed. The playing here is such a masterclass in moving through harmonic ambiguity with total clarity. This is partly because this standard is harmonically complex, always cylcing through substituted progressions and almost never settling into its home key of B♭ major. It is full of interesting chromatic modulations, and tonal misdirections. But the melody over the top ties it together so much. Sometimes it feels to me like a forerunner of Wayne Shorter's Infant Eyes. When I first transcribed this it amazed me how much Keith Jarrett is always thinking of the melody rather than the changes, and weaves this into all kinds of harmonic possibilities.
The thing that always stands out for me in Jarrett's playing is that he never reduces the complexity of Stella but instead illuminates it. There is no sense of finding the the right scale for the moment. All 12 notes of the octave are always in play. His solo flows naturally through modulations to keys like G major, E minor, and C minor, linking tonal centers ornate phrasing and pushing against the beat with this positioning of notes.
A PDF of the solo can be downloaded here. Or here is the link to a MuseScore format. The best way to learn this solo is to create a recording of it in Transcribe and then learn to play along with the recording. Memorise it and play it at the speed and level that you are comfortable with. I have also used the MuseScore file to export the data to MusicXML and put into Logic Pro, to create ear training excercises which can be a great thing to do, to really go deeply into the sounds of the notes against the harmonies. Lots of different options you can explore.
And here is a couple of choruses of my own solo on this great standard. Enjoy