Although it’s important to point out that those two are vastly different.
Sovereign citizens deliberately misinterpret US laws to (in their minds) escape jurisdiction. Reichsbürger are actively planning a coup to overthrow the government, install an actual emperor and go back to feudalism.
Sounds ridiculous but they are connected and prepared surprisingly well wich make them a real threat, not just a funny curiosity.
…and at the same time supporting racist and anti-migrant narratives to “fight” the fascist AfD. Which, obviously, just strengthens that narrative and hence the AfD.