When you try to get an empty minecart to travel through a nether portal, it works perfectly fine, but it doesn't work if there is a villager inside the minecart. I haven't tested this with any other mobs yet. In my situation, I am transporting villagers from the nether back to the overworld.
Related issues
is duplicated by
MCPE-89480
Nether portals
MCPE-122087
Villager in minecart portal bug
MCPE-134554
multiple entities can't teleport at once in the same nether portal
MCPE-169037
Minecarts with passengers fail to go through end gateways
MCPE-181884
Entities with passengers cannot use Nether Portals, End Portals and End Gateways
MCPE-183355
Ridden entities cannot go through nether portals
MCPE-184993
Can't Go Through Portals With Ridable Stuff
relates to
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I don't think that's a bug, that's how it's been for a while.
migrated
relates to MC-67
DeeFeeCee
Affects 1.19.22
X1Crafts
As Skaijie mentioned, this relates to MC-67 which has recently been fixed in Java, so it can also be considered vanilla-parity.