Possible htaccess configuration issue for HTTPS websites by WP Fastest Cache plugin? [closed]

Do these lines mean HTTPS urls will not be cached?

Well, it certainly means that on most servers that have an SSL cert installed, the URL will not be rewritten to /wp-content/cache/all/<requested-URL-path>/index.html. If that means the cache will be bypassed, then yes, it prevents caching.

The idea of not caching HTTPS requests would seem to be very outdated.

However, the WP Fastest Cache plugin page does include “SSL support” as one of its features and further down the page explicitly states: “Yes, it is compatible with Http Secure (https).”. So, there is perhaps more to this than that presented here?

WP support query posted by the OP (currently unanswered):
https://wordpress.org/support/topic/use-of-rewritecond-https-on/