Can I clean up and tape old unfinished drywall in the garage?
Yes you can clean patch and clean then texture to your hearts delight. I have done this in both garages and bonus rooms that the paper was yellow with age. After wiping down I taped and muddled then sanded wiped down and shot the texture, it has turned out great and just this little bit of work has added thousands to the appraisal, so it is worthwhile and will look much better. If the surface is oily a Tri sodium phosphate (or replacement chemical) may be needed for the wipe down just don’t go two wild with the water.