This tree (Minnesota) started losing its bark about 1.5 years ago and it's getting worse. There is also an area on the tree that looks to be rotting. I could seal the hole but now I'm worried the tree is a lost cause. Any thoughts?
Based on the loose bark at the bottom of the large scar (photo 1), I think your tree has a canker that is not healing. It may also be responsible for the large scar, although that's unclear (could be a torn-off branch or other damage). If the wood is squishy in that area and smells sour, then it's definitely rotting. The hole in photo 2 looks like it goes through to the heartwood and that the tree is hollow.
My non-arborist opinion is that this tree is dying and is becoming unsafe. I strongly recommend that you contact an arborist (NOT a tree-cutter) and get a professional opinion.
Your tree is dead ,it just doesn't know it . It may take years to fall down. I had an oak about twice that diameter that did not fall for 15 years after shelf fungi started growing at badly damaged bark. I trimmed off dead branches from time to time to prevent them from falling and causing damage.