In the documentation it says use "CleanroomGenerator:^." to make a void but in 1.18 it doesnt work. Multiverse is accepting it and keeping it but going to an area with no chunks will start genrating terrain like normal.

can confirm I also have experienced this

I relased genarators with multiverse dont worked for the default world set in the server.properties.

Ah yeah if you want world generators for the default world you have to configure it in your bukkit.yml not MultiVerse.

https://bukkit.fandom.com/wiki/Bukkit.yml#*OPTIONAL*_worlds has some info and examples for reference.