There really isn't a pattern. Basically if they have a pro Mac ready to go or something that needs developers to prepare, they'll announce it at WWDC.

2021: nothing

2020: M1 Macs

2019: Mac Pro

2018: nothing

2017: iMac Pro, HomePod

2016: nothing

2015: nothing

2014: nothing

2013: Trashcan Mac Pro

2012: MacBook Pro 15" (first retina Mac)

2011: nothing

2010: iPhone 4

Considering the fate of the Trashcan Mac Pro, HomePod, and iMac Pro.... maybe it's OK that they didn't introduce any new hardware at WWDC this year !!

That being said, the iPhone 4, Retina MacBook Pro, and M1 were transformative - nothing was the same afterward.

(Probably not coincidentally, they also all required major software revisions!)