Twilight Forest (Dim:7) is already not kind on servers when it comes to generation, and with RC on top of it, it gets butchered.

This is how the config looks, copied directly from the wiki:

# Dimension Expression that will be checked for every single structure. Use this if you want to blacklist / whitelist specific dimensions that shouldn't have structures. [default: ]
S:universalDimensionMatcher= 0 | 1 | id=-1

This is how the console looks:

Also tried other config lines, like

S:universalDimensionMatcher= !(dim.id=7 | type=UNCATEGORIZED | id=7)

and structures still generated (observed ingame)

It seems to work for me. The only thing the option doesn't cover is custom trees - which would explain the log too.

Is there any way to disable the custom trees within the dimension?

Is there any way to disable the custom trees within the dimension?

I would love to know this as well. Perhaps custom trees should be either included in what is affected by this config option, or a new config option specifically for trees needs to be added.

Was going to submit a ticket for this myself. Glad to see I'm not alone with the issue.