I assume with a regular set card like this they’ll just add it to the pop when the first one is being graded. With every card, someone had to be the first to grade it eventually. I do indeed see a lot of missing cards for the Champion’s Path pop report: www.psacard.com/pop/tcg-cards/2020/pokemon-sword-shield-champions-path/181110
A bit odd it isn’t available as option when submitting the card, despite the current pop-0, though. I’ve never submitted any cards to PSA, so not entirely sure how it works when you’re the first to submit a certain card.
Ran into the same problem with cards from the 2021 Japanese Rapid & Single Strike sets. I just manually typed in the card name/number and I believe once they get to grading it they will add as Quuador mentioned.
I dont know about these sort of cases, but you likely won’t be the first submission. I think a lot of these cards will be in the bulk backlog already and nobody decided to grade this card express.