I can’t use plugins due to private data

I’m not sure I follow you on this one. What has a plugin that simply injects your analytics code into the header or footer of your site got to do with this “private data” you mention?

…it looks more likely I need to manually tag all the pages.

Well, that’s an option… I just don’t get the privacy angle ??

You’d typically put the code into your theme’s header.php or footer.php file only once, and it should appear in all pages on your website.

And you probably should create a child theme, else any future update of your theme will override any change you made to theme files.

All the best!