We have a lease property where one of the bedrooms was converted to an office by the previous owner. There is no closet. There is a window and there are two entrances to the room which have doors attached.
To be considered a bedroom it must have a closet and an interior door that could be closed for privacy. An outside window would be nice, but dont consider it a requirement.
With no closet, it would be considered an extra room. Especially for leasing purposes a prospective tenant would expect to have a closet in a bedroom if it was advertised as such. You may want to consider converting it back to a proper bedroom or advertise appropriately as an extra room and let prospective tenants decide for themselves how they want to use it.
Generally, to be considered a bedroom, a room needs a closet, exterior window, and an interior door. The Houston MLS has a true bedroom count and count of total rooms that could be used as a bedroom. A study with no closet could be noted as an additional room that could be used as a bedroom.