I don’t know about Finland but here in Germany, motorised vehicles must have a Straßenzulassung (road approval) in order to be legally operated in public traffic. So, rather than generally allowing any motorised vehicle that is not within the scope of current laws, any motorised vehicle that is not within the scope of current laws is not allowed on german public roads.
And I’d be kinda surprised if it was much different in other countries, except for maybe the US (I’d still be surprised, just not as much).