10 cm/4 inches of water is a lot for a fruit tree. My question is how long your tree was flooded? A few hours or a few days? Also, after the flood, how long the soil continued to be wet?

Usually pear is more tolerant to excessive water than cherry or plum. However, if your tree was flooded and sat in wet soil for several days, the chance of it dying is high.

Trees in the property behind the wall look like peaches and they appear to do well. Were they flooded, too?

The tree is fine and I wish mine were in so good a shape.

The pear tree was in water for like 2 days.

Well, we also have 2 cherry's and 2 plums, neither of them are dying or showing any signs of dying.

Yes, that behind is another fruit garden and those are peaches. They were flooded, but with around only 5cm of water.
We also have a peach that was flooded and its fine.

We have a lot of fruit trees that were all flooded the same and only the pear seems to be dying,

I don't think the water has anything to do with it. The tree is obviously under stress and it might be caused by having to carry so much fruit. Your pears look ready to harvest, and I wouldn't be surprised to see it recover after the fruit is gone. I'm assuming that you haven't deprived the tree of water because of the brief flood.

I didn't know what to do, so I picked all the pears off the tree. They're much smaller than last year, but after I ate one and they tasted like a normal ripe pear.

I'm hoping now the pear tree doesn't die

I don't think the flood caused the problem, either, after hearing that other fruit trees have done well in the same situation.

This pear is under stress. I don't know why. You'll have to wait and see. Hope it will recover fully.