I don't see any files that would match these URLs on your account. If these are supposed to be dynamically produced by WP, then WP is probably just broken (not uncommon for WP...). Did WP update perhaps? Your site also has a lot of complicated rules in the .htaccess due to some cache plugin that was installed, it's completely possible that plugin broke.
Also, when was the last time these pages did work? I remember visiting this site as part of researching another issue a few months ago, and it had the same issue then (subpages didn't work), so that makes me question when this last worked (or if this has ever worked).
The only thing I can suggest is to try is turning off the proxy ("orange cloud") on cloudflare, but I'm not sure that's going to do much in this case since the issue is that the server can't find the content. I'd usually suggest renaming .htaccess so its ignored too, but in this case that may just make the issue worse, especially if you're relying on rewrite rules for pretty URLs.