Built a garage, top part is Airbnb rentals- how to input Asset(s) in Turbotax since not a residence?

Yes, this is considered a rental property. You can deduct the proportionate share of the property taxes, insurance, and other expenses including depreciation for the rental space, against your rental income. All income/expenses are reported on a Schedule E.
 

You will need to set up the rental under the Rental and Royalty section. When setting it up, indicate that you are renting a part of your home. You will be asked questions on the number of days rented if less than the entire year. For the personal use days, you will enter 0 if you did not ever use the rental once it was placed in service.

The rental section is quite extensive.

You would include the garage if it was available for use by the rental. If for your personal use, then it is not included as part of the rental.

Here is a TurboTax article about Rental Property
 

You still set this up in the Rental & Royalty Income (SCH E) section. If the garage is not for the use of the tenant, then it's not included in the percentage of your entire floor space, which includes the house you live in. You'll need to pro-rate anyway, unless the the structure has a completely separate mortgage, completely separate insurance policy, and completely separate property tax bill.