Creating a new Impress presentation will show available built-in presentation template chooser dialog. This dialog should has an icon for Additions dialog which contains available Presentation template from LibO Extension site.
Step to reproduce:
1. Create a new Impress presentation (File menu > New > Presentation)
2. A presentation template chooser dialog
Heiko Tietze committed a patch related to this issue.
It has been pushed to "master":
Resolves tdf#137671 - Extensions on Impres start-up
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:
Affected users are encouraged to test the fix and report feedback.