/execute as @e[type=item,nbt={Item:{id:"minecraft:minecart"}}] run data merge entity @s {Item:{tag:{CanPlaceOn:["minecraft:rail","minecraft:powered_rail","minecraft:detector_rail","minecraft:activator_rail"]}}} still doesn't work with a mod's advice.

I'M SORRY TRYASHTAR im bad at commands.

This will be the last one as long as nothing goes wrong.

The command said in the title does not work at all. Even after breaking the minecart and EXECUTING the command AFTER the minecart has been broken doesn't work. I have an attachment so you can view what happened. Please don't yell at this. I'm sorry. 😢