Hello @frans-blok,
After step 4 (In the Property column, click GA4 Setup Assistant, then click Get Started under I want to create a new Google Analytics 4 property, then click on Create and Continue.), your migration is completed, and it is safe to skip step 5, as Google seems to skip it for some accounts.
Here is the official documentation for reference :
https://support.google.com/analytics/answer/9744165?hl=en
I have checked your website, and it seems that the plugin installed the required tracking code correctly, and soon, you should start receiving data in the graph.
Please be advised, it might take up to 24 hours, for newly created accounts to collect data from Google servers.
Also, Your old data (from universal analytics), will not be transferred to your new GA4 account, and Google offered no way for this migration to happen.