You cannot get that R 30 which is 9 1/2" into 2x6 ceiling joists.

Yes, which is why I’m asking if there are other insulation options that are thinner and could possibly work?

Spray foam

Pull up the plywood. Add a 2x on top of the joist to increase their depth. Replace plywood.

Thinking about it now closed cell foam would more than likely get you there but it will end up being quite expensive. Location dependent I would venture $7-8 a sq ft for a smaller quantity and I could still be completely wrong.

Depending on how your attic area is used, you may be able to augment your existing insulation by blowing cellulose on top of the attic floor to a depth that adds the required R-value.

With the 2x6 bottom chord on the attic truss for a usable floor area, you should be insulating the roof plane and kneewalls. That will be much easier to furr out the top chords to get your required depth for your selection of batt insulation. RED is furring/blocking, BLUE airspace.

Closed cell spray foam.