Q1: Does this card's On Play When Digivolving effect trash a card from my opponent's security stack even when they have 6 or more security cards?
Yes, it does.
Lv.5 Cyberdramon BT21-024 U Ultimate | Vaccine | Cyborg [On Play] [When Digivolving] If your opponent has 5 or fewer security cards, they place 1 card from their hand as the bottom security card. Then, trash their top security card. (Rule) Trait: Has [Dragonkin] Type. --- Inherited: [Your Turn] This Digimon gets +4000 DP.
Lv.5 Cyberdramon BT21-024 U Ultimate | Vaccine | Cyborg [On Play] [When Digivolving] If your opponent has 5 or fewer security cards, they place 1 card from their hand as the bottom security card. Then, trash their top security card. (Rule) Trait: Has [Dragonkin] Type. --- Inherited: [Your Turn] This Digimon gets +4000 DP.
Lv.5 Cyberdramon BT21-024 U Ultimate | Vaccine | Cyborg [On Play] [When Digivolving] If your opponent has 5 or fewer security cards, they place 1 card from their hand as the bottom security card. Then, trash their top security card. --- Inherited: [Your Turn] This Digimon gets +4000 DP.