âWhen wasâ is used to ask about the state of something in the past, typically focusing on a singular subject, while âwhen didâ is used to ask about a specific action that happened in the past, requiring a verb following the subject to complete the question. Technically âbeâ is a verb, so it isnât wholly wrong in a broader structural sense, but this is a case where English has an exception that takes precedence. Youâll note that âbeâ â âthe state of beingâ â is the exact scenario we use for âwhen wasâ structure instead, because to âbeâ something is to be in a specific state.
âWhen did the owner found Tantabus.ai?â would be a valid structure. You are asking about an action that was taken, not a state of being.
âWhen did Tantabus.ai start?â would be another valid structure. This is still a query about an action being taken, not a state of being.
When talking about a FUTURE event, using âwhen willâ instead of âwhat wasâ, as âWhen will Tantabus.ai be founded?â is correct. This rule only applies to past events.