Yes, as long as the owner does not object. There is no supplement to pay, not least because sharing the driving makes for safer travel on long journeys.
Every secondary driver must meet the same rental conditions as the primary driver.
Secondary drivers must be added to the rental agreement at checkin. For a classical rental, at the beginning of the rental, each additional driver must present his original license (no copy), that the owner will take in picture recto verso.
NB: Once the checkin was signed, you won't be able to add a secondary driver via the mobile app.
For a Drivy Open rental, to add a secondary driver, you have to send pictures recto verso of the driver's driving license to :
for cars registered in France : firstname.lastname@example.org
for cars registered in Spain : email@example.com
for cars registered in Germany : firstname.lastname@example.org
for cars registered in Belgium : email@example.com
Please indicate the rental reference in your email.
Once the secondary driver is added, he can drive anytime during the rental, the primary driver doesn't need to be present every time the secondary is driving.
NB : Only the main driver can sign the agreement at checkin and check-out.