I don't understand why this relatively simple conversation is taking so long. Let me summarize:
1. Standard built-in meeting recording tools (like Zoom, Meet and Teams) all give a warning to other participants, and have done so for years. These are the gold standard for what users expect from recording-enabled tools, because they've been (essentially) the primary game in town and I can bet that everyone reading this conversation has encountered the warning at least once before Otter etc. came along.
2. If you want to build your own meeting recording tool that joins the meeting as a "participant" (or as an add-on to a real participant's own machine) then it seems like a good idea to try to mimic the same warning UX for the other participants. At worst you're following "best practices" and at best you're insulating yourself from a lawsuit like this one.
3. I don't know what you're talking about when you mention Otter (the subject of TFA) because I clearly see Otter notetakers join as a participant. Or per the docs: "Otter Notetaker can automatically join your Zoom, Google Meet, or Microsoft Teams meetings and transcribe your meetings in real-time." I can't see any reason why, as a separate participant, they would be technically unable to display a written warning on the video feed and/or emit an audio warning.
4. From perusing Otter's site, it looks like you can also upload a Zoom recording (which will cause Zoom to emit the standard warning) or you can sync in an Otter app, which requires Zoom Admin and presumably has capabilities like "warn the other users" since the integration is pretty tight.
5. Even if the software is running purely locally, I imagine there are ways to insert a warning into the meeting. Maybe in a few cases there is some technical reason it's absolutely impossible that I don't understand! But frankly, I do not believe that the lack of warning is purely due to technical limitations, since Otter Zoom participants also don't recite one. I'm fairly certain that even tools that purely use local feeds, there is likely a way to emit this warning to other users if you want to badly enough.
6. If this is a purely technical argument about the limitations of the product used in that one specific case, then let's have it.