You don't have permission to submit the post.

Please note that this is not an error, this is in compliance with WordPress rules

Please read more WordPress Roles and Capabilities: https://wordpress.org/support/article/roles-and-capabilities/

So to have the right to submit articles, you need to have role permission from the Contributor up.

-> So how can all users post after registration?

So that all users after registering as a member can post articles, you just need to set the default role for registered members to be Contributor.

Navigate Dashboard -> Settings -> General -> New User Default Role -> Contributor.

Don't fret about it, these are great features of WordPress. Think about it, for particular users that you don't want them to submit posts anymore, then you just need to lower their role to Subscriber.