I want certain web pages blocked (within my country) by my Govt on a website that uses HTTPS on all pages. My Govt agrees that the specific URLs need to be blocked but expresses helplessness as their ISPs claim they can't selectively block HTTPS URLs but must block the entire website/domain / sub-domain which will cause genuine users to be affected. The prominent website in question has refused to take down the impugned web pages despite notices from my government and law enforcement requests.
No, the ISP cannot block specific HTTPS protected pages because it cannot determine which page is being accessed.
HTTPS does not hide the server that is being accessed, because it needs the SNI (Server Name Indication) to be on the clear, so the server can know which certificate to use on the connection. Once the handshake is established, everything else is encrypted, including which page you are requesting.
So the ISP have two non-optimal ways to answer: don't block anything, or block the entire server.
Encrypted SNI is a thing for the future. It is part of the TLS 1.3 specification, but isn't something that can be enabled by changing a configuration option on the webserver. It needs changes on the DNS records, and support from the webserver. It still don't have widespread support among webservers and web browsers, and is still not mature enough for high-traffic servers to adopt it.
ESNI would help hide the domain you are accessing from your ISP and government (depending heavily on your network configuration), but would not help the ISP selectively block pages on the domain.
Just for completeness, there are actually ways to achieve this, but they are usually the work of totalitarian regimes who want to eavesdrop on everyone's conversations and/or block content not matching the "party line", and of course won't be done "just for you": force all users to install an alternate root certificate, and have all traffic to that site to go through a proxy which will present a TLS certificate signed by that alternative root before forwarding to the original server, except for the page in question of course.
Like others said, for most cases inspecting TLS traffic would require installing certificates or even some software, which don't applies for most people. In the other hand, depending on how you consider blocking, there is a method which can make it possible:
There is a study that shows that in some cases HTTPS encrypted content can be identified: there is a paper (PDF) that shows that's possible to build a database of fingerprints which can be used to identify HTTPS-protected Netflix videos in real-time. There some limitations, such as taking some time to identify the video: "[...] the majority of the identifications occurring less than two and a half minutes into the video stream.".
It doesn't identify which exact URL was being accessed and cannot be used to block content completely, but if the URL just points to a video and the content that need to be blocked is after the detection margin, it can be used to detect when someone started to watch it then block connections to the server after that. In the context of totalitarian regimes, it could even be used to find those who watched videos against it. In the context of ISPs, it could be used to guess if some user-watched some popular video then sell this data to advertisers.
As this paper dates from 2017, before TLS 1.3, is possible that this method isn't working anymore. I hope.