If you want to share a file to collaborate with colleagues but
work in a public team, you can set up a private channel within
a Microsoft team to limit and add members that you want to
collaborate with. Open the team you want to set up a private
channel in, click the ellipses ... and click Add Channel.
You can name the channel, then select the privacy setting as
private, then click Next to confirm. You can then choose to
add members you want to work with in the private channel or
skip this step for now.
You can also add additional members to your new private
channel by clicking the ellipses ... in the top right hand corner
and selecting Add Members. Then enter the members of the team
you would like to add and click Done.