creating new iam user leads to "unknown error"

hi,

i am following the aws amplify tutorial ( https://docs.amplify.aws/start/getting-started/installation/q/integration/angular/ ) and i want to create my first iam user via console ( https://us-east-1.console.aws.amazon.com/iamv2/home#/users ) but i get an "Unknown error" every time i press the "Add users" button (see screenshot https://imgur.com/a/SX3KrGw ).

trying to open "Account settings" ( https://us-east-1.console.aws.amazon.com/iam/home#/account_settings ) leads to the same problem.

i am logged in with the root user and don't know what to do. Can you help me or point me in the right direction to solve the issue?

Thanks and greetings!