Header + Footer disappered, can't safe page, WP Update messed up totally

My domain: www.kuestenwerber.de

Hi Support-Team,

after the Update of Brizy some months ago, my Header and Footer was gone. I tried to do your troubleshoot tipp of doing a minor change to the header/footer and safing it new. However then I had the next problem: I could not refresh my page. It was stating that I had a page open somewhere else, which is not the case.
Today I tried again, then I saw there was a wordpress update and now in the middle of the update the entire wordpress dashboard changed to a debugging site stating this: 

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Notice: Function _load_textdomain_just_in_time was called incorrectly. Translation loading for the brizy-pro domain was triggered too early. This is usually an indicator for some code in the plugin or theme running too early. Translations should be loaded at the init action or later. Please see Debugging in WordPress for more information. (This message was added in version 6.7.0.) in /mnt/web501/a1/90/52210790/htdocs/STRATO-apps/wordpress_02/app/wp-includes/functions.php on line 6114 Notice: Function _load_textdomain_just_in_time was called incorrectly. Translation loading for the wordpress-seo domain was triggered too early. This is usually an indicator for some code in the plugin or theme running too early. Translations should be loaded at the init action or later. Please see Debugging in WordPress for more information. (This message was added in version 6.7.0.) in /mnt/web501/a1/90/52210790/htdocs/STRATO-apps/wordpress_02/app/wp-includes/functions.php on line 6114 Warning: Cannot modify header information - headers already sent by (output started at /mnt/web501/a1/90/52210790/htdocs/STRATO-apps/wordpress_02/app/wp-includes/functions.php:6114) in /mnt/web501/a1/90/52210790/htdocs/STRATO-apps/wordpress_02/app/wp-includes/pluggable.php on line 1435 Warning: Cannot modify header information - headers already sent by (output started at /mnt/web501/a1/90/52210790/htdocs/STRATO-apps/wordpress_02/app/wp-includes/functions.php:6114) in /mnt/web501/a1/90/52210790/htdocs/STRATO-apps/wordpress_02/app/wp-includes/pluggable.php on line 1438

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Now I can't even go into the dashboard to make you as a user. My host is strato. Do I need to check with them? Do I need to start from scatch? 
Helpless regards, Leslie