I've been wondering the same thing. The last chance for such a coin will be in the December release (if there is one). There was a limited release last December, so there is a possibility that a 2020 coin in this series will still be released - but I'm not holding my breath!
It seems that it might have been replaced by the Maple Leaf coin in the 2020 O Canada! six-coin set. It's also a 1/2-ounce silver coin and its Matte Proof finish would be visually similar to that of the previous Specimen finish coins.
If that is the case, however, it will cost $15 more to keep the collection going as the 2020 O Canada! coin is $50 CAD vs. last year's $35 price!