Is there a official answer to this? There are a lot of discussion online on this topic and I cannot find one conclusive answer

For example, Armorer has access to Shatter spell, can I put it in Spell Storing Item or not?

For Armorer it says "These spells count as artificer spells for you, but they don't count against the number of artificer spells you prepare", and in spell storing item it says: "and you store a spell in it, choosing a 1st- or 2nd-level spell from the artificer spell list that requires 1 action to cast"

So I guess I am asking is "spell counting as artificer spell" = "spell on the artificer spell list"?

Quote from fott25 >>

Is there a official answer to this? There are a lot of discussion online on this topic and I cannot find one conclusive answer

For example, Armorer has access to Shatter spell, can I put it in Spell Storing Item or not?

For Armorer it says "These spells count as artificer spells for you, but they don't count against the number of artificer spells you prepare", and in spell storing item it says: "and you store a spell in it, choosing a 1st- or 2nd-level spell from the artificer spell list that requires 1 action to cast"

So I guess I am asking is "spell counting as artificer spell" = "spell on the artificer spell list"?

I'm not aware of an official ruling on this specific issue, but a similar question was answered in the Sage Advice Compendium here: https://www.dndbeyond.com/sources/dnd/sac/sage-advice-compendium#SA012

Essentially the question was whether a Bard could use a spell scroll containing a spell that they got from their Magical Secrets feature but which wasn't normally on the Bard list. The ruling is that yes, they can, because that spell counts as a Bard spell for them. Therefore, it stands to reason that Artificers' subclass-specific spells count as being "on the Artificer list" for them, since the same wording is used.

In my opinion something counting as an "artificer spell" for you means it counts as on the "artificer spell list" for you.

Sage advice seems to support this when answering a question about Spell Scrolls which a character can only use if the spell appears on their spell list:

Which spell scrolls can bards understand—spells from the bard list only, or spells from the bard list plus spells from Magical Secrets?

A bard can use any spell scroll that has a bard spell on it—including spells gained from the Magical Secrets feature, which are treated as bard spells for that character.

So while I couldn't find a RAW case it seems RAI something being "a  [class] spell for you" means it's also "on the [class] spell list for you."

For reference the rules on Spell Scrolls (2024):

A Spell Scroll bears the words of a single spell, written in a mystical cipher. If the spell is on your spell list, you can read the scroll and cast its spell without Material components. Otherwise, the scroll is unintelligible.

Spell Scrolls (2014):

A Spell Scroll bears the words of a single spell, written in a mystical cipher. If the spell is on your spell list, you can read the scroll and cast its spell without Material components. Otherwise, the scroll is unintelligible.