Template manager has a button which opens the extensions site. This should be replaced with the internal dialog.
Heiko Tietze committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/core/commit/9eaaf97ab32068a619b5c36772619b7e66268800 Resolves tdf#137477 - Access templates via tight extensions It will be available in 7.1.0. The patch should be included in the daily builds available at https://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: https://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.