Nothing should have changed in Opus 12.
If the general setting is on but not taking effect, you most likely have a folder format overriding the global setting in some or all folders.
It's also possible the size calculation thread has got stuck somehow, in which case fully exiting Opus (via File / Exit Directory Opus) and then opening a new window for a folder on a local drive would cause the calculations to work again, but they would stop working later (including for the same folder).