4 official rulings from Bandai, last ruled Mar 28, 2024. Straight answers to how this card actually resolves.

If this card's <When Digivolving><When Attacking> effect activates when digivolving, does it activate again in the same turn when attacking?
No, this effect is a <Once> effect, so it can only activate once.
Ruled Mar 28, 2024
Does this card's <When Digivolving><When Attacking> effect prevent my opponent's Digimon from suspending even when I activate an effect such as a "suspend 1 of your opponent’s Digimon" effect?
Yes. They can't suspend by effects regardless of whether they were activated by you or your opponent.
Ruled Mar 28, 2024
If an opponent's Digimon with no digivolution cards enters the battle area after this card's <When Digivolving><When Attacking> effect activates, can that Digimon suspend?
No, it can't. This card's effect targets "all of their Digimon with no digivolution cards," therefore even if your opponent's Digimon with no digivolution cards later enters the battle area, they are still affected by this effect.
Ruled Mar 28, 2024
If an opponent's Digimon gains digivolution cards through digivolution or some other method after this card's <When Digivolving><When Attacking> effect activates, can that Digimon now suspend?
Yes, it can now suspend.
Ruled Mar 28, 2024
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Questions and answers are Bandai's official rulings, collected and translated by the DigimonCardGame Wiki community and reused here under CC BY-SA. Card names and card text are © their respective publishers; Combalo is not affiliated with Bandai.