I know Tachiyomi (and associated forks) are a popular way to browse and read manga within the community (myself included). This change means that the Tachiyomi app will no longer include access to installation of all but a select few extensions. Specifically, the only extensions allowed going forward are the “bring-your-own” services. You can see the new extension list here.

Based on some of my searching, this change seems to be in response to the threat of legal action by Kakao Entertainment (a Korean webtoon company). Tachiyomi had recently removed a couple extensions from their app (mangadex being one of them), but this change is sweeping.

Going forward, if you have extensions currently installed on your device, they are going to stay there, but will no longer be maintained. So, if something breaks for the service it is communicating with, then the whole thing breaks.

The latest version of Tachiyomi added the ability to add external extension repositories. So, this enables the option of other groups maintaining extensions in the place of the Tachiyomi devs.

Edit: For more context, there are two relevant discussions on the [email protected] community. One about the mangadex extension specifically, and the other about this latest move.