Farmer villagers are slow to do their job, ends up planting on some sections, and/or just doesn't work, or move at all.

They just look down for the entire day.

This proof is done below a villager Trading hall, considered as a "Village"

He has his inventory full of Potatoes, but all he does is Plant on those specific blocks, and then, look at that block for all the day, without nothing else happening.

Here's also how the farm is set up.

And a video about the Farmer not doing anything, even throught he has his inventor Full of Potatoes, and all of the blocks are farm lands. 

SVID_20230603_161928_1.mp4

Update:

It seems the entity only "works" When a block near him gets updated, like, breaking a dirt block, and placing a New one.