In Wolfenstein: Youngblood, there are three special types of Kraftwerk doors, each requiring a different weapon to unlock (with an ability needed for opening grates). Though not all that important for finishing the game, they are necessary for getting all the collectibles.
The weapons you need are the Laserkraftwerk, Dieselkraftwerk and Elektrokraftwerk. The first weapon, the Laserkraftwerk, is found in Brother 1. Head to the prison section underground and locate a sealed office. You can drop into the office via the ventilation shaft and pick up the weapon from the nearby armory. It’s worth noting that sealed doors that require the Laserkraftwerk can also be opened by using the heavy weapon Lasergewehr.
The second weapon, Dieselkraftwerk, can be found in Brother 2. Locate the yellow network door with the keypad and look behind it. There should be a room beneath the garage where a robot is located. Destroy the anchors restraining the stairs and you’ll find the Dieselkraftwerk. Use it to open doors that have orange markings on them.
The third and final weapon, Elektrokraftwerk, can be found in Brother 3. Upon reaching the lab with Super Soldiers and shooting ranges, look for an open vent. This will take you to a test room that contains the Elektrokraftwerk. Unlike the other doors, you need to use the Elektrokraftwerk on a nearby power box to get through rather than on the door itself.
For grates, you need the Crush ability which costs five ability points. Unlock this when the game starts and you should have no problem breaking through grates to reach different paths.