PSA:
If you have category 1-4 certificates that expire 12/31/21, check-out needs to be on or before 12/31/21. So you have only 2 more nights to use those.
If they were earned from Chase as your annual free night, Hyatt will generally exchange for 10,000 points if you have stayed 10 nights with Hyatt this year, or have status, YMMV.
If you are not eligible for the points and no travel plans, your best option would be to use for a staycation at a brand you have not yet stayed at. This will get you closer to a brand explorer award.