I want to sell the studio I bought 10 years ago, which was my main residence until 3 years ago. My banker tells me that I still benefit from the capital gains exemption. Is this correct?

No. To benefit from the capital gains exemption when selling a home other than your principal residence, you must :

• the seller must not have owned his or her principal residence, directly or through an intermediary, during the four years preceding the sale;
• the seller must undertake to use the proceeds of the sale to purchase a new principal residence.

In your case, as you owned your principal residence 3 years ago, you do not meet the 1st condition for exemption.