Python 3.5. as well as Python 3.6 is EOL. As toolforge is moved from Stretch to Buster release which comes with Python 3.7 it is planed to drop Python 3.5 support soon but we should have a data base how often outdated Python releases are still used. It would be useful to have some statistics for that.
See older requests made in T242157 and T286867 for previous release changes.