I have an Office 365 E3 plan and make extensive use of SharePoint Online and ODFB. I also use the consumer OneDrive. My workstations include PCs and a Mac. This problem concerns only Office for Mac.
Office for Mac apps having version 16.29.1 have the following problems: (A) File/Open does not fully refresh, i.e., the files showing in the target directory of either SPO or ODFB are not current; (B) because of the previous issue, the apps cannot open current files from SPO or ODFB (because they are not listed as available); and (C) they cannot save to SPO or ODFB, because they do not see appropriate document libraries or directories.
If I log in to O365/SPO and download a file or sync a directory, the file or folder will sync correctly. But then when I try to open a downloaded file, the app says that uploads are blocked.
I have disabled the firewall on the Mac and set it to different configurations to see if any of that would make a difference, but it doesn't. The firewall does not seem to be relevant. I have also tried this with different routers/locations, and that doesn't make a difference.