What happened?

jetpack can't put in curios back slot. even allowed_slots = ["back"] in setting of create_jetpack-common.toml (server side).
1.20.1

Loader

forge

Mod Version

create_jetpack-forge-4.0.0

Minecraft Version

1.20

Relevant log output

No response

Hey, you still have to enable the jetpack in the slot using a datapack, you can read about it in the last section of the README.
I'm actually thinking if that config option is misleading and I should probably remove it completely

I think I will also create an example datapack for this usecase

datapack has been created, you can download it here

I mean the elytra slot fabric mod is also almost just a datapack

Yes, it solved. and I have learned how to solve it now! thanks for all these reply.

how would I do this for trinkets instead of curios?

Thank you. Turns out an even easier way to make it work is by editing the elytra slot fabric mod for people who don't want to make a datapack, adding two lines of text in one of the files makes it work.

That's described in the README file of the fabric repository