WITHOUT THE EXPERIMENTAL MINECART UPDATES THE MINECART FEATURES WON'T WORK


ONLY WORKS ON 1.21.11 OR LATER BY DEFAULT BECAUSE THE minecartMaxSpeed command was renamed max_minecart_speed

for adding minecart improvements to existing worlds see this guide: https://www.youtube.com/watch?v=MmLHVI-U5xM
Summary:
- Make a world backup
-  open your world in an NBT Editor
- Add a list tag under Data and rename it to enabled_features
- under enabled_features add a string tag called minecraft:vanilla
- under enabled_features add a string tag called minecraft:minecart_improvements
- this datapack should now load w/o error but you can also confirm the Mojang's minecart improvements are loaded via the max_minecart_speed gamerule