Dear People of the Future,
I had this exact problem in 2019 on macOS in 2019, even without an Unraid Upgrade, and this is the forum post that comes up on Google. Here is how I solved the same problem of "The folder “whateverFolder” can’t be opened because you don’t have permission to see its contents."
First:
1) Run the "New Permissions" utility for each share you are struggling with. You can do this by clicking Tools ->"New Permissions" under the "Unraid OS" header.
2) Leave that browser window open, It took my computer about ~4 hours to cove 1.5 terabytes of data, so just *be patient*
2.5) at this point you will notice you still can't access the folders, even if you disconnect and reconnect to the server. Don't worry that's normal.
3) RESTART YOUR MAC, I know, its crazy, and Macs can go months without restarts, but for whatever reason macOS resets some permission cache that reconnecting to the server won't reset.
4) Everything should work like normal.
4.5) If 1-3 doesn't solve your problem for every share, just do it again, one share took two attempts to get it to work.
1 +2 +3 should solve your problem.
Happy Unraiding