If your MacBook Air is slowing down, don’t rush into replacing it with a Mac Pro, that’s a $7K+ workstation meant for film studios, not day-to-day use.
Most slowdowns on Airs come from limited RAM, storage nearly full, or too many background processes, which are usually fixable without dropping thousands. If you meant MacBook Pro, that makes more sense, but Apple won’t “roll over” your Affirm loan, you’d need to either sell your current Mac privately or check if Afrm lets you open a new plan.
Also, check storage usage (System Settings > General > Storage), login items, and Activity Monitor for anything eating resources, you might be able to get your current Mac running smoothly without upgrading.