Hello colinrowe2,
My name is Veejay, an Independent Advisor and a Microsoft user like you and I'll be glad to help you.
As of now, setting password for files and folders is not yet available but its up for a vote:
https://microsoftteams.uservoice.com/forums/555...
As a workaround, you can use Private Channels.
This will create a channel that only a few members will have access to, these permissions is also inherited to files and folders.
https://support.microsoft.com/en-us/office/crea...
Please let me know if you have any questions or concern.
Thank You