title: How to make Thonny use installed Python 3.9 (macos)?
body: <p>I'm on macos 10.14.6, with Thonny 3.3.3 / Darwin 18.7.0 / Python 3.7.9 / Tk 8.6.8. I'm using Thonny to program a RaspPi Pico.</p>
  <p>Thonny crashes a lot - apparently because of bugs in the tkinter tk library. (According to searches - <a href="https://stackoverflow.com/questions/57435896/tkinter-crashes-computer-after-macos-10-14-6-update">Tkinter crashes computer after MacOS 10.14.6 update</a> )</p>
  <p>I've installed the official Python 3.9.1  - but it seems that also has tk 8.6.</p>
  <p>Can I get Thonny to use Python 3.9.1?  And will that help stop the crashes?</p>
  <p>Or, can we get Thonny to use the older system installed Tk, which is 8.5? Will that help?</p>
  <p>Thanks.</p>