I'm testing out M365 for a few users to replace an on-prem fileshare. I've shared a folder with both of the users. One user can access the folder and enclosed files with no problem. The other user cannot. They can see the folder in the "Shared With You" page (Left Menu-->Shared-->Shared With You). However, when they click the folder, they get the page to request access. I've had them request access multiple times and approved it each time. They still have the same issue.