I will be looking into it in Norway (EU regulations) but I know for a fact that the interpretation of the regulations vary widely from country to country.
In other words, there will be different requirements for each country.
As Norway is a very EV positive country it might be easier then for an MX ice bike, and I know some are getting those registered so it should be possible (here).
Also, I know I will ned E marked light all around including front, rear, brake, signals, and number plate light, and one mirror at minimum size. I will probably get a small LI package to supply the lights for shorter trips.
Here it's quite common to remove blinker and mirror and mostly getting away with it.