What you want is the service manual. Owner manual should be implicit. OBD port can work for some cars, for some of the data. But other cars do have specialized gear they require to either access either reset some stuff in some of the car's computers.

Yeah the owners and service manuals are two very very different things. You won't be performing much maintenance with the owners manual besides the absolute basics, like checking your oil.

The cheap OBD2 readers lack the vast majority of data and tools you would want to use for service as well.

There are aftermarket options but most manufacturers want you to subscribe to their service tools - often charged per monthly plus an additional a fee per VIN it touches. These cost in the hundreds to thousands. It can be pretty frustrating as a shadetree mechanic.