DNS happens before HTTP and HTTPS. If you block at the DNS level it will work for both HTTP and HTTPS URLs.

That page you linked seems to confirm this, and that Pi-Hole works just fine blocking HTTPS.

That's true, but instead of empty ad being server (as in case HTTP), HTTPS request timeouts and increases loading time for many pages, because the page waits until all JS loads.

Another problem is that some browsers will retry failed request several times (Chromium) effectively prolonging the time before final error is confirmed.

More about HTTP retry can be found here https://tools.ietf.org/id/draft-nottingham-httpbis-retry-00....

To sum it up. Using pi-hole had a negative impact on my browsing experience because HTTPS pages were more less buggy/slow.

HTTPS requests only timeout if your setup doesn't reject them (also described in your first link).

True but only if the add is served off a different domain.