How to fix that new users show up again in subsite of a Multisite?

That its expected behaviour, you have to manually add the user to the site and select his role, you go to All Sites, Edit a site, then select the Users, tab:

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Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)