Well, I've been trying to create a culture for a few weeks using the Uncle2Fire guide as a reference, I know it's Outdated, but it's the best reference I have as a modding newbie. If there is any more updated tutorial I would like to know if it exists. Now these are the errors that I usually have and that even so Unity does not notice them if you try to test the mod as it does with others:

I don't even think I have directly touched many of the elements that appear there and in fact I will share the mod file for anyone who wants to take a look at my little mess. I would really like to know how to fix this as I think eventually this will be like the CultureSuperPack but with my own ideas and stuff obviously so I have a lot to learn.

The Mod: https://drive.google.com/drive/folders/1JhwelNT8BgSPH3qEbDqJTdQLDQWGegdj?usp=sharing

Maybe I've made some obvious mistake, but I'm too new to all of this to realize it. I have redone the mod from scratch about 5 or 6 times.

Usually using the official culture as a baseplate is best, you can also go to Discord to find him

In fact, I use an Official culture as a base, in this case the Olmec, and I still have those problems. Maybe I should listen to you and enter the Discord, but I will leave this post open in case someone answers something else or I find a solution to share here for those who arrive later.

To be honest I 100% ignore all unity error messages and only care about error messages in game and in the diagnostic files

Well, for those who come to this post, I leave you the solution that they gave me in Discord:

1. Cultures now require some new mappers for things like their traits or unit traits.

2. It's better to hit "Build" and start the game rather than "Build And Run" as trying to start both may cause errors.