Again , dependent upon where you are based in France , several French owners make the trip across the Channel to get their cars serviced at BHM near Sevenoaks in Kent (about 40 minutes drive from the ferry/tunnel terminals)
Keith , and others there, have a lifetime of experience with Morgans, so I am sure they can sort your car, however I accept this is not legal for you to leave the country under the current lockdown rules , and you probably want it done before the easing comes along.
Just a few ideas about the reluctant revving :-
1 Has the car been standing for some time prior to the sale? If so the fuel may be old, and can sometimes give rise to peculiar issues of rough running. A refill with some fresh fuel is sometimes all that is needed. Try the "Italian Tune Up" once on new fuel, hold onto the gears rather than changing up early , get the revs to clear anything.
2 Do the rev rises cleanly when in neutral , or only under load? If the former then I suspect you will need someone with Rover diagnostics as the T16 engine is fully integrated computor (ECU) controlled. If the latter I would be looking for intermediate misfire issues, I think I read recently of a UK member whose T16 engine ignition leads were breaking down under load. You can look for this by running the car in a dark garage , spraying a fine mist of water vapour over the engine , and looking for any electrical tracking. The Rover diagnostics will throw up any fault codes which can be followed up.
3 Have a look at the service records , when were the spark plugs last replaced? Do the coil packs look OK?