Stream Channels can only be created based on these two Channel access types. It cannot be created specific on a Team Site without Office 365 Group.
As is quoted from this document: Groups and channel settings in Microsoft Stream:
Channels are an organization method for videos, but not a permission method. Channels don’t have any permissions on their own.
When you create a channel, you decide whether it’s a companywide channel that anyone in your organization can add and remove videos from, or if it’s a group channel where you can limit contributors.
If you want to restrict user access to Stream contents/Channels, a group is required.
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