I’ve discovered some time ago trying to create a team via flow that you can’t copy content to the team due to that the corresponding channel folder in sharepoint aren’t provisioned til you actually click “files” tab in Teams! I’m now trying to do the same via graph but it’s the same! Anyone found some way around this! Like some kind of trigger that will provision the folder?
I would look at provisioning the folder in SPO using Flow, then create the channel in Teams - that way, Teams will 'connect' to the existing folder.
I've not checked recently, but I seem to recall it was a case of having flow create a file - e.g. dummy.txt with a path of /foldername/dummy.txt - this creates the folder - then you can delete the txt file.