Expected behavior is villager continues to loop back and forth without dismounting the cart can see it in the pag5zonda farm.

does this happen with vanilla as well? Can you provide a screenshot of the setup?

I just checked in vanilla, when a villager riding a minecart falls on top of or runs into the side of an end gateway portal, he doesn't dismount when passing through (1.15.2 Vanilla).

Just tried out this setup with fabri-carpet - the villager doesn't dismount

don't think how carpet would be affecting villagers and minecarts. It will be good to get some info about your setup and confirm its not a setup issue.

probably not an issue.