I don't think I would go for a non-Polestar solution because of the complexity of integration with the vehicle electronics. I note from the manual that connecting something to the towbar connector changes the behaviour of a number of items (cameras, CTA, etc).While it has been done else where, speaking to Polestar on the phone they said no one in the UK is trained to do the install.
It's not that hard ... the only "hard" part is wiring up the electronic release button. So I'm not sure if this is some BS to stop people ordering without and then getting Volvo to retrofit or true. Giving them the benefit of doubt I suspect they meant "No one has been trained to install specifically a tow bar on the Polestar 2"
If you are not fussed over the official semi-electronic one, I'm sure you could get a removeable one fitted for a lot cheaper from a third party.
I think I will wait until next year to decide what to do - that might include identifying a Volvo dealer in Germany that has been trained and going there if no UK dealer is available.