I've got this error at loading:

Error :

[08:52:48] [ERR  ] Error occurred while handling event 'tags.items': TypeError: Cannot find function getObjectIds in object items:forge:ores/copper. (server_scripts:unify.js#205)

It seems that getObjectIds does not exist in the TagWrapper class: https://mods.latvian.dev/books/kubejs/page/tageventjs

Minecraft version: 1.16.5
Forge : v36.2.34
KubeJS: 1605.3.19-build.299
UnifyTags: 5ceb46a

i can confirm, i have it on my private server/pack as seen in this log

The official wiki is very outdated and is missing a large number of functions in it. Here's your function right here:
https://github.com/KubeJS-Mods/KubeJS/blob/08a786a8cb6bd70e7f9e8d6ae30009821a45a6c5/common/src/main/java/dev/latvian/mods/kubejs/server/TagEventJS.java#L196=

It seems like they renamed it from getAllItemIds to getObjectIds and that's where this problem lies. I'll attempt to call whichever function is available.