disable users ability to add/remove videos from company wide channels?

PhilC42  Yes, it is a default feature you can not deactivate, see: https://docs.microsoft.com/en-us/stream/groups-channels-overview#companywide-channels

Channels in Stream have no security level, no permissions you can assign to. Properties are only a name, a description and an image. To achive what you want you have to create a public group (Trainings) and  channels inside this group. This channels are globaly visible for all users. If the user is not an owner or a member, the video can not be removed from channel. The trainers should be owner and the switch "Allow memebers to contribute" can be off. Or you have one or two owners and the rest are members with the switch on. Than all team member can edit the video permissions. I think this is you scenario: https://docs.microsoft.com/en-us/stream/groups-channels-organization#companywide-top-down-sharing-few-contributors-everyone-can-view