If the freehub is Shimano and only 7 speed, with no spacer behind the cassette, there is a chance it is an RM30-7 hub. You can get a replacement freehub body. You should remove the axle and ball bearings and use a 10mm, I think, Allen wrench to remove freehub body. It should have external splines on the freehub body, but you can check pictures online.

If it is a not Shimano, you’ll need to take it to a shop, or figure it out looking online. There is a chance it is a Formula hub. You might have to find a complete hub and transfer the body.

You might be able to soak the freehub body in solvent, after removal, and see if the pawls free up and start engaging. I’ve done this and dripped Phil’s oil in after it dried out.

John