Steps to reproduce
Spawn a villager.
Sell it items once.
Buy an item from it.
Expected result
Buying from the villager gives it twice as much experience toward its next level as selling to it, as it did before 1.16.
Actual result
Selling to the villager gives it twice as much experience toward its next level as buying from it.
There is a glitch with villagers,when trading villagers get more xp when giving them items, see the photos I have attached you will understand it better...
Confirmed by looking through the fisherman and fletcher trade tables in the 1.16 vanilla behavior pack. Every trade where these villagers buy items for emeralds gives twice as much XP as the trades at the same level where they sell items for emeralds. In 1.14 and earlier it was the opposite, they got more XP when the player bought from them. The older behavior was more intuitive and challenging, as it usually meant you had to buy their wares to unlock the best offers.
It seems this change was made along with the fix to MCPE-47141, but I do not know if this change was correct.