A closer look into Gmail search semantics revealed that I could simply use the keywords “in:spam” to refer to the all messages under my SPAM label.
Knowing this, I set up a filter to automatically mark all new SPAM messages as Read within Gmail.
I have chosen to do this as I don’t want to see when a new SPAM message arrives and be tempted to check if it is legitimate. I find that Gmail’s SPAM filter is nearly 100% accurate so not constantly checking the SPAM label improves my productivity. But this is subjective and this operation or method may not be suitable for your related needs.