Your website is infected by Malware.
Hackers are using your WordPress website for ‘spamvertising.’
This causes an insane traffic spike. Spam emails are sent from your server with links to existing or new pages that are created by the hacker.
Spamvertising can vandalize blogs, websites, forums, and comment sections with hyperlinks to get a higher search ...
You have a couple of options -
Install a plugin that adds GTM for you. This makes it very easy, but it does add another plugin to the site. Site Kit supposedly slows down a site more than you would expect.
Make a copy of header.php and put it in your child theme folder. Now you can make edits to this file without the edits being overwritten when the parent ...
Hopefully, this helps.