I have no idea if this is a feature where there are too many enchantments on a bow and I cannot enchant any further, but I do not remember that ever being announced as a feature in any recent major update. The bow you see in the first slot of the anvil I have already "enchanted" with infinity. I assumed it was a visual bug, but that was soon disproved by the fact that it consumes arrows when shot.
I think I need to apologize for something. In the previous snapshot 19w35a, there is a bug (that was fixed recently) where honey level would not go up in bee hives. I made a bug report about it, and was too eager to actually get it fixed that I ended up not searching for people who have already reported it. For that, I am sorry.
I did some good searching this time, and no one seems to have the same problem (which is why I am thinking it might be a feature). If it IS a feature and/or was already reported and I did not do enough searching, I am sorry for that as well.
Infinity and mending are not compatible.