ai to obj conversion is possible in the sense that it is possible to export shape or letters made using Adobe Illustrator to a 3D object saved in OBJ format, typically for transfer to other software or 3D printing.
This can be done with Illustrator's Export asset function, but in the past users used Photoshop as well. AI assets can be imported to Photoshop as smart objects. Once this is done you just select the layer of the object you wish to export and use the option to form a new 3D Extrusion from the selected layer (in 3D menu), which can you can then save in OBJ format using the Export 3D layer function.