From Ryzen 7000 forward, the third number is the core generation, and this weird mixing is only true outside desktop too (see the 5600X3D). That's also because

From Ryzen 7000 forward, the third number is the core generation, and this weird mixing is only true outside desktop too (see the 5600X3D). That's also because AMD keeps die shrinking older generations of processors (i.e. the Steam Deck), but not as far down as Zen 4 because they're still capacity limited there. So it makes sense to keep 6-7nm designs alive for longer.