My mother’s laptop has been running as fast as a turtle on a snail going uphill for a long time now. Everything has been done to it, including formatting it and installing another, less cumbersome OS, but nothing improves. I have an HHD available, I have done some tests and it does work.
Would changing the hard drive do any good?
You could try getting a SATA SSD. Those are slower than M.2 or NVME-based product, but it will serve you well. Try looking for a low-storage solution for now. Maybe 128 or 250GB should work fine. Since you have a spare HDD, I think it’s okay for now.