Due to regulatory issues, it is much more difficult to install F-Droid on some Android distributions than Jami, and they complain about any third-party apps that can install apps independently, so I think it’s a terrible idea to have someone else download an app market for the sake of a chat app.
In my case, the official F-Droid website has been blocked, so I had to download the apk file from a third-party website, but the installation package extracted from the F-Droid app has a strange different signature than it, so that the system makes the installation fail.