TileEntity

Looks like vanillafix and Tiquality-FAT-1.12.2-GAMMA-1.8.1-124.jar are conflicting - remove one of these mods

Make a test without chisels-and-bits-forge

Add such a crash-report with sites like https://mclo.gs/

There is an issue with lootr Try an older build: https://www.curseforge.com/minecraft/mc-mods/lootr/files/5166263 If the issue persists, backup the world and remove this mod Join the world again - if there is no issue, put the mod back in

There is an issue with tfcthermaldeposits

Add crash-reports with sites like https://mclo.gs/ Remove chaosawakens

ImmersivePortals is mentioned - is there a change without it?

Is there a log or similar?

Yes

Does it work without Optifine? If yes, replace it with Embeddium/Oculus https://www.curseforge.com/minecraft/mc-mods/embeddium https://www.curseforge.com/minecraft/mc-mods/oculus

strawgolem is not working - remove this mod

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

Add the crash-report or latest.log (logs-folder) with sites like https://mclo.gs/ and paste the link to it here

Also remove randompatches

It is an issue with SolarFluxReborn - maybe a conflict with AE2 Report it to the creator

Add the new crash-report

Add this mod: https://www.curseforge.com/minecraft/mc-mods/advancements-debug

Contact the support of this site

Common mods are Industrial foregoing, botania, create or immersive engineering - but these are not up-to-date for 1.21.1

Make a test without Rubidium

Remove randompatches

Replace Journeymap with this build: https://www.curseforge.com/minecraft/mc-mods/journeymap/files/5616347

Make a test without modernfix

Worldedit Forge is currently only available for 1.20.4 and older

Add the new log