Alternatives to big-name proprietary remote-lecturing tools
BigBlueButton is software designed for remote teaching. It makes it possible to teach using videos, share slides, annotate them, do breakout rooms, etc., and can be integrated with Moodle. It is open-source and can be self-hosted.

It is apparently not easy to set up, but can be done, and can scale to dozens of participants provided they don't all have their webcam set up (e.g., only the instructor and a few people asking questions share the webcam).