We are planning to move to Python 3.10 for the upcoming release of Mantid v6.8.0 in mid-October.
The changes are still under review, so are not available yet in the nightly releases. However, you can test them by installing packages built from the development branch either from Conda:
mamba install -c "thomashampson/label/python310" mantidworkbench
or you can download the standalone installers from the following Jenkins build:
Any feedback is very welcome. We would like to encourage early testing so that any problems caused by the Python upgrade can be addressed in time for the release.
Tom (on behalf of the Mantid team)