I added the Yung's family of mods to a version of Mr. Beardstone's Create Perfect World 2.0 on my own server.
I was troubleshooting and updating the mod pack when I started crashing.
I back tracked my mod updates and found that the Supplementaries Mod update greater than 1.20-3.1.18 caused the game to crash (client side testing).
Once I downgraded to 1.20-3.1.18 the game loaded correctly.

However, the log file suggests that YUNGs Caves Biomes is to blame for the crash. In my experience it's usually NEVER the mod that reports the crash that causes the issue but another mod that has already screwed something up. Looking further down the log file you can see where the Supplementaries is encountering some kind of ERROR on load (undefined at this point)

So, YUNGs Caves & Biomes has some issues with Supplementaries v1.20-3.1.19 on Forge 47.4 and MC 1.20.1.

I have not isolated the two to see if the error is present when only these two mods (plus necessary libraries) are loaded.

What version of Cave Biomes are you on? If you update to latest version, it should fix the issue of Cave Biomes being falsely reported for other crashes, so then you can more easily see the real cause of the crash.