Is it possible in minecraft 1.16.5 to add/remove veins from the exavetor with crafttweaker or kubejs or some outher way?
And if so can you pint me in the right direction?

Our veins are done like vanilla recipes, so you can use a datapack to add, replace or disable them.

If you know how vanilla datapacks work, doing compat for IE is very easy, you just match our folder structure data/immersiveengineering/recipes/mineral and you can throw replacement files there.

The original files can be viewed here:
https://github.com/BluSunrize/ImmersiveEngineering/tree/1.16.5/src/generated/resources/data/immersiveengineering/recipes/mineral

Never used datapacks before and cant seem to get it to work. I'm using multimc
I hava made a file named diamond.json in
.minecraft/saves/[save name]/data/immersiveengineering/recipes/mineral/diamond.json
I have also tried it in the [save name]/datapacks
And the content of the json file is
{ "type": "immersiveengineering:mineral_mix", "ores": [ { "chance": 0.6, "output": { "item": "minecraft:gravel" } }, { "chance": 0.4, "output": { "item": "minecraft:diamond_ore" } } ], "dimensions": [ "minecraft:overworld" ], "weight": 8, "fail_chance": 0.2, "sample_background": "minecraft:netherrack" }
atleast i cant find it in the ingame manual or if i run the /ie mineral list

Yeah of course that isn't gonna work, because that's not the correct file path at all. Datapacks go into saves/(world)/datapacks, are a subfolder or zip file there, which must contain a pack.mcmeta file and then a data subfolder which is where your filepath should continue.

But it's not our job to teach you how a vanilla datapack works. Minecraft has a wiki for that:

https://minecraft.fandom.com/wiki/Data_pack