Trying to link to a php template file but its blank

get_header() and get_footer() are WordPress functions, not native PHP. If the code snippet you’ve posted is the entire content of tos.php, you’re not loading WordPress at all, the functions don’t exist, and so tos.php is throwing a fatal error. It’s likely that your web host is configured to not display fatal errors, so you see an entirely blank page.

Further: Gutenberg is an editor, and shouldn’t affect the display of pages on the front end. If you’re trying to specify that a given post or page should use your tos.php template, you should have a look at the template_include filter.