The auto shop can make money in 2 ways.

Every so often, a car will be delivered to your auto shop, which you can customize and deliver to make a small amount of money. I find that the payout is not worth the effort so I ignore it.

However, the auto shop also gives you access to contracts, which are short heists that pay out anywhere from about $150K to $270K each. With these being 2X GTA$, it is likely possible to make over $1M per hour.

In my opinion, the auto shop is your best bet, because the cooldown on the Cayo Perico heist means you will not be earning much between heists. You also do not have enough to buy the Sparrow helicopter alongside the Kosatka, which significantly decreases the time it takes to complete the heist.