It looks like it hasn't been pruned in decades!! And that would be where I'd start. Proper pruning of fruit trees - especially spur bearing fruit trees - is very different from pruning ornamental trees and shrubs and is difficult to communicate by words only :-) One really needs or will benefit best from a hands-on approach so a class - often offered by nurseries or other retailers/orchardists in your area - may be the best approach. You can sometimes find good info on YouTube but just as often find garbage - for a novice, I wouldn't recommend.

After some good pruning, you will need to educate yourself on fruit care, including any necessary spraying for diseases or insect problems, thinning fruit, possible fertilization, etc. And when it starts to produce fruit again, identification. It could be a seed grown variety that just does not produce a very palatable fruit!

If not a locally adapted variety or there is another issue making fruit unacceptable, such as it being a random, unselected seedling (pippin) that doesn't happen to be any good then no amount of care is likely to result in good fruit.

For starters, see "Pruning to restore an old apple tree"-

https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec1005.pdf

Thanks for all the suggestions

Might I also suggest, don't plan on getting this thing back in shape and producing well in a year. In my experience, it will take several years to get the tree where you want it and maybe even more to get production back to acceptable.