Hi @StephenScollay,
You can either use the py3.9 version of Houdini 20, and the engine will work, as Fabian says, or you can edit the tk-houdini engine to make it work with the Houdini 20 that uses python 3.10,
see Tk-houdini engine for Houdini 20
I hope the SG team makes an official release of it soon
Cheers
Donat