Since 2023, Capital One has a rule that you can only get a signup bonus once every 48 months. They’ve now tweaked the language of the terms to combine the Venture X and Venture cards into one family for the 48 month wait:
You are not eligible for this product if you have received a new cardmember bonus for the Capital One Venture card or the Capital One Venture X card in the past 48 months.

It’s not clear if this language is yet being enforced, but worth keeping in mind.
Hat tip to CobaltSunsets
