Sinitsina allegedly tried to apply to Cup Final but wasn't allowed:
Как стало известно «СЭ», российская фигуристка Ксения Синицына пыталась подать заявку на участие в финале Кубка России.
m.sport-express.ru
I don't know how reliable this source is though. But if it's true, then it's really not nice from RusFed, considering that many notable skaters could go despite not completing in Cup events and Kseniia would definitely deserve it after her successful performances at Nats2020, JGP events and Youth Olympics.
Edit: one of the reasons why Kseniia was not allowed to jump over qualification criteria could be the fact that she is only on reserve team, not the main one. But it's still a pity, especially after Gulyakova withdrew, they could have at least sent Kseniia as substitution.