The floor or the door is not level.

A piece of the wood to the right side is missing when the old tiles were removed.

The door panels are easily removable. Next would be the bottom track. The wood piece should be removed and replaced. The tile installer can offer options to replace the wood.

@dan1888. The tile installer has finished the tile installation and left. Why should the bottom track be removed, and the wood piece be replaced? The bottom track is the frame of the door and I think it would be difficult to remove, It is a vinyl door.

Below is a picture of the old piece of molding/quarter round that was covering the wood at the patio bottom. It is not exactly a quarter round, and I could not find similar one at any stores.

You might be missing a threshold. These are often made of aluminum or wood. Feel free to google videos on replacing these.

So, is your door out of level, or is your floor out of level?

@eam44. Can you explain what "is your door out of level, or is your floor out of level?". Thanks

Hi. Sure. The red line on the left is longer than the red line on the right. Assuming the door was installed to be level, that means your floors are out of level. This can happen in older homes, but it can also happen if the door (sill or bottom plate - the terminology gets complicated) is rotting and your door is no longer level. It would be good to know which is the case.

@G & S Floor Service. The wood that is at the bottom of the patio door is 3/8" high and 5/8" wide, a flat piece of wood to cover it will not work.

Take a oscillating tool and cut it off and install a 3/4" quarter round. If, you think it can't be wrapped with a 1/4" material. In fact, that would be the best option, is to cut off, flush to the door and floor, then cover it up with a quarter round. You would need to shape the quarter round to follow the taper that you have there, it's doable .