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?
100% yes if it’s failing. Buy an ssd and revel in the new speed, don’t do another spinning disk.