Besides 'not much', that is.
My experience with making things for this game is that all of the information on what has been experimented with and what works is very scattered and finding it all takes about as long as the learning itself.

I was wondering if any creators here already had any insight on making traits, when so few have been published.
Have newer methods and/or tools ever made it more viable?
Script modding is definitely at the fringe of my abilities so I know it won't be easy either way.

For reference, I'd like to make another dietary preference trait like Vegetarian, pescetarian specifically. It feels promising that it could mostly be a clone of that, but I still have the hurdles of safely getting it ingame and adding a new recipe filter.
Any insight is appreciated and would restore my will to stare at ILSpy any longer.

Maybe contact these users on MTS, they have experiences
https://modthesims.info/showthread.php?t=674064

Arsil made a custom trait manager, beta, but here in the description you find your answer why there are not many, if you delete them not right, you can destroy your ongoing game.

So because a lot users also naturally forget to read again uninstall notes for their mods, before removing it, they will run into many problemproblems. I personally would never install custom traits.
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https://modthesims.info/d/593251/testin ... nager.html

I've seen a bit of that but didn't realise there was a tutorial within the description! Thank you.

The uninstall thing doesn't bother me too much personally, I'm not in the habit of pulling script mods out mid-save anyway.
Finding the easier ways to do things seems to be my thing, so I shall post an update if I make any progress.

I am interested in this topic as well. I want to make a few hidden traits for disabilities. I'll check out those links and if I succeed (or learn anything) I'll report back too.