Pear Tree Leaves Are Yellow
A few things appear to be going on. The little holes are probably sapsucker damage. The holes may have girdled the tree, preventing nutrients from traveling to the roots to the top of the tree. The holes have also created a space to let disease into the tree - like fireblight.
The presence of fungi and the rapid leaf decline suggests that this tree is dying. It probably used up all stored energy producing flowers and initial leaves and is having difficulty transporting nutrients to the leaves. While it could have fireblight also, both the condition of the tree..girdling holes, fungus and leaf drop...makes it unlikely that this tree will survive. (The lower branches appear black and crooked.) There is no cure for fireblight. And it is already likely in the trunk of the tree.
If you have other pear trees, I would recommend removing it to prevent disease traveling to other trees. If it's the only tree here is some suggestions for slowing down the progress of fireblight: https://extension.umn.edu/plant-diseases/fire-blight