The title says everthing. I tried it with 5.1 and 5.2 of flans but both times it crashed.

Please post a link to a crash log. Use https://paste.ee/

https://paste.ee/p/xHJUq
Note: I also tried it with no other mods than flans.

Looks like your game has something registered to key code 316 which LWJGL doesn't know about.

Could you look into your options.txt file, have a look at what's using value 316 as a keybinding and let me know what that key is on your keyboard?

its : < used by most control stuff i dont need.
key_Bomb Key:316
key_Gun Key:316
key_key.backpackloader.load:316
key_key.backpackloader.edit:316
key_key.backpacks.permission:316
key_key.saveToolbarActivator:316
key_key.loadToolbarActivator:316
key_nei.options.keys.gui.enchant:316
key_nei.options.keys.gui.potion:316
key_nei.options.keys.gui.prev:316
key_nei.options.keys.gui.next:316
key_key.jei.toggleOverlay:316
key_key.jei.focusSearch:316
key_Look at Gun:316
I hope this is wath you meant.

Similarly related (as a friend's been having this problem with the same crash log), I've been having an alternative crash when hopping into a vehicle: https://pastebin.com/WY2EyNCR

The player screen shows a void as if the vehicle was incredibly far away and the chunks didn't render.

Ohh i forgot the void there is nothing its almost like the chunk that im in is gone (i cant remember if the vehicle ist gone too because i dont play with the flans mod if the vehicles dont work).

Never mind i reinstalled minecraft and it works fine :)