also I feel like, the number of people that hop on the incident call are almost always related to the category of the incident, sure you can always break out to a separate room, but often the person would have already realised the impact and the weight of the incident
If whoever feels like it can "hop on" the incident call and stay on it, regardless of whether or not they can contribute to the investigation, then the IC needs to do a better job. Granted, usually this is for lack of institutional competence; I've been one place where the IC role was taken seriously, and incident response there ranged from solid to legendary, where most places never rise above "cautionary tale." But nonetheless.
It is one thing if they are being disruptive, but I don't see a problem with observers.
For this thread, the fact that some people may feel scared to share a screen or participate if the group is too large, again that is for the IC to control. But I wouldn't kick anyone else just for lurking, there may be a good reason and I'm not going to call out every one on the call asking why they are there, that is just as disrupting.
TIA
It does depend somewhat on the situation and the organization, and on the role; IC engineers observing for familiarization is fine, VPs joining never is. My approach is that the incident call is for those actively involved in the investigation or who have been invited to join by those who are, including engineering ICs who wish to observe for familiarization. Meanwhile, stakeholders not directly participating in response receive updates from the incident commander via a separate (usually Slack) channel. Managing that communication is also part of the IC role, whether directly or by delegation.