Make minecarts act as chunk loaders using redstone.
Minecarts will only load chunks after you manually (or by using redstone) enabled them.
First create a "chunk loader creator" by putting the following pattern in a dispenser. When powered, any minecart in front of it will toggle its chunk loading ability. If the minecart is an active chunkloader, it will emit particles.
You can change the radius in which chunks around the minecart will be loaded by changing the "minecartTicketRadius" gamerule to any value between 1 and 16, 1 meaning only the current chunk the minecart is in will be loaded.
A chunk loading ticket created by a minecart will always expire 5 ticks after it's creation and will only be refreshed once expired.