I would really like to switch from UltraPermissions to LuckPerms, but I do not want to re-do all my permissions, and currently migrating from UltraPermissions to LuckPerms is not supported.

If you send me the UltraPermissions jar I can take a look at implementing it. :)

I'd have to talk to TechsCode because I believe I am not allowed to share the jar :(

Err yeah, he'd probably prefer if you didn't post it publicly, but you can PM it to me on Discord if you like.

https://discord.gg/luckperms

Isn’t there a public API?

Nope...