Hi @Järbrink David ,
In the screenshot of your post, this is the site permissions, not the folder permissions, please make sure the folder inherits the site permissions.
If the folder has no unique permission, however "Everyone except external users" group still not work, please edit the URL by adding the following string to the end of it:
/_layouts/15/people.aspx?MembershipGroupId=0
On the list, select the user, open the Actions menu, and then select Delete Users from Site Collection.
Then re-grant the permissions to the file or site for the group.
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