How do I make a folder always be sorted by Last Modified Date?

I tried Folder->Folder Options-> Save button, but that didn't help.

Thanks,

That should be all you need to do, assuming the sort order was how you wanted it before you saved it.

Make sure the format lock is not turned on on the status bar. The lock icon should be opened, not closed.

When testing, close any open Opus windows and test using new windows to ensure no temporary changes are being remembered by the old windows and complicating things.