It means the inscriptions hack hasn't been patched in any version of Core. Alao Core v29.1 introduces the multiple outputs bug which accidentally allows more than one OP_RETURN per transaction.
Knots has mitigated the inscriptions hack and doesn't have the multiple outputs bug.
Miners can still directly accept junk into blocks through things like slipstream, though it hasn't been a huge problem so far. Partly because they have ToS that don't allow illegal content.
LibreRelay is another method. I'm not sure how much it's being used.