From the lender's perspective, the only thing that matters is if the borrower intends to physically live in the property when you apply for the mortgage. Mortgages are either classified as owner occupied (the borrower lives in the property) or non-owner occupied (the borrower does not live in the property) at the time you submit your loan application and the occupancy status can change after your mortgage closes. For example, many people buy homes using an owner occupied mortgage, live in the property for several years and then move out and rent the property. If these people were to apply for a mortgage to buy another home to live in, the new mortgage would be classified as an owner occupied loan on a primary residence even though they still own the property they are renting out and remain on the mortgage for that property.
In your case, as long as you do not physically reside in your old property anymore, you should have no issue qualifying for an owner occupied mortgage to buy another home, even though you remain on the mortgage for the old property you plan to rent out. And as long as you intend to live in the new property the mortgage will be classified as an owner occupied mortgage on a primary residence. Please note that it is also possible to obtain an owner occupied mortgage on a second or vacation home so you can have owner occupied mortgages on multiple properties, although the mortgage rate is typically higher for second or vacation homes.
We provide a comprehensive overview of the differences between owner occupied and non-owner occupied mortgages on FREEandCLEAR for you to review.