Connection of double garage and separate workshop. Looking for ideas

How about a garage door opening to the back into the garden towards the workshop?

Then you would use the garage as a driveway the few times a year for the vintage cars.

It would probably be a relatively cost-effective solution since you could use a manual door there. Additional cost compared to a built-back wall < €1,000.

I can't find your "suggestion" in the plan?

How about a carport instead of a double garage?

(Assuming the answer is no... anyone with classic cars certainly wouldn't expose their youngtimers to the harsh wind and weather ;) )

I cannot find the "proposal" from you in the plan?