There have been various request for donations over the years. And I am considering setting up a Patreon project at some point in the future. But at the moment there probably aren't enough users to make it worth while. Piano Booster was always held back by the fact that it did not work well on Windows due to the dreaded Latency delay when using the Microsoft windows sound generator -- but now that has been fixed by including fluidsynth sound generator with piano-booster.
I have lots of future plans for Piano Booster including doing lots more YouTube post with piano lesson which should get lots more users and at that point i might setup a PianoBooster Patreon project at some point.