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

If I have a [Kiriha Aonuma] in play, do I get to choose either "Reveal 4 cards from the top of your deck. Add 2 cards with [Blue Flare] in their traits among them to your hand. Place the rest at the bottom of your deck in any order" or "return 1 [MetalGreymon] from your trash to your hand" for this card's <On Play> effect?
Yes, you can choose one or the other.
Ruled Mar 28, 2024
Can I use this card's <On Play> <When Digivolving> effect to add a card to my hand when only 1 card with the [Blue Flare] is among the 4 revealed cards?
Yes, you can. In such cases, you add as many cards to your hand as possible.
Ruled Mar 28, 2024
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