Modify twentytwentyfour template with PHP

I need to password-protect certain templates (category, archive) in twentytwentyfour for my site with 1000 members, each with their own username-password. For WordPress “pages” I have been able to make “php” versions of the “page.html” template that I can assign to the page manually. But for “category” or “archive” the same technique doesn’t work – WordPress looks only for “html” templates in the template hierarchy. How can I make WP recognize my php versions of templates; or is there another way to password protect for 1000 separate log-ins? Thanks.