TileEntity

Use such a pre-made modpack as working base - allow content management and add new mods one by one

Did you try older builds? https://www.curseforge.com/minecraft/mc-mods/unionlib/files/all?page=1&pageSize=20&version=1.21.1&gameVersionTypeId=1

The config folder is in the same folder as the mods folder if you are using the original Launcher, then it is C:\Users\NAME\AppData\Roaming\.minecraft\config\

The config of UnionLib is invalid Delete the config of it (config folder) - if there is no change, try other builds of UnionLib

You are using Create 6 - some addons are not compatible with it Remove all addons and add these one by one littlecontraptions is mentioned - keep this one removed

Remove vanquisher_spirit

Add the latest.log from your logs-folder

Yes

Make a test without the aether mod

Try Embeddium instead

Completely reinstall the modpack If there is no change, create a forge profile and add the mods one by one or in groups Or use a pre-configured modpack as working base and add new mods

Make a test with another Launcher like MultiMC or AT Launcher: Create a Forge 1.20.1 profile (forge-47.4.0) and start it once - close it in main menu Then copy the mods from the curseforge mods folder to the new launchers mods folder and test it again

These can be ignored

Hm, I have no idea - nothing mentioned

Add crash-reports with sites like https://mclo.gs/ Furnection (ls_furniture) and Mysticbiomes are not working - make a test without these mods

Maybe try other builds If there is no change, the maybe another mod is conflicting - but not mentioned

Let the friend remove the mod starlight

Does it work without ImmersiveEngineering?

Make a test with another Launcher like MultiMC or AT Launcher: Create a Forge 1.20.1 profile (forge-47.4.0) and start it once - close it in main menu Then copy the mods from the curseforge mods folder to the new launchers mods folder and test it again

Add crash-reports with sites like https://mclo.gs/ Did you make mod changes? The crash refers to ImmersiveEngineering Did you connect Immersive Engineering stuff with contents of electrodynamics?

Is the RAM allocation high enough (-Xmx value)?

And without Ksyxis?

Update your AMD/ATI drivers - get the drivers from their website - do not update via system

There are no issues - what exactly is not working? Does the server crash or is it unjoinable? If you refer to the red error blocks, these can be ignored - these are common recipe and loot_table error - mods are overwriting these

Remove mods one by one or in groups until you find the mod causing this issue