I no longer have traverse as a mod in my modpack but I still get this error:
04Apr2022 03:12:31.261] [Render thread/ERROR] [net.minecraft.util.registry.DynamicRegistries/]: Error loading registry data: Unknown registry key: minecraft:fallen_trunk_placer; Unknown registry key: traverse:none_foliage_placer

or errors like this
[30Mar2022 02:08:43.592] [main/ERROR] [net.minecraft.util.registry.DynamicRegistries/]: Error loading registry data: Unknown registry key: minecraft:fallen_trunk_placer; Unknown registry key: traverse:none_foliage_placer

How exactly do I prevent errors from a mod that are not even in my mods folder

Please upload a full log so I can properly investigate

Isn't this normal if a generation mod is removed? I think it can happen whenever new chunks are generated adjacent to chunks owned by the removed mod.

Closing as I think it's normal when generating adjacent chunks after mod removal.