Maybe I overlooked it if it says so in the documentation, but my fishing rates seem to be abnormal. I have caught 210 items, and zero of them were treasure. Treasure with a default rod should account for 5% of the catches, and for 210 items without 1 single treasure drop that would be a 0.002% chance of happening. The Junk rates seem to be normal, at around 10%.

Another weird thing I have noticed is that the more mobs you kill the better enchantments their loot have. For example, I got probably 300 bow drops before one had flame, then I started getting flame bows pretty consistently after the first one. Same for higher level protection enchantments, I never got level 4s until I got one then started getting them regularly. I don't see anything about drop rates being altered in the documentation either.

Nevermind, I didn't realize the dimensions of the pool used to fish matter now. Still confused about the weird drops from mobs though, but it is a non issue.

Fishing has required "open water" since 1.16 to discourage afk fish farms.

The improving mob drops is probably the result of increasing regional difficulty: https://minecraft.wiki/w/Difficulty#Regional_difficulty.
Essentially when you spend time in one place, the mobs that spawn there get stronger, so they are more likely to have weapons/armor and for it to be enchanted.