It could be negotiated as an investment, but that only benefits Adobe. Figma wouldn't want it (would you want your biggest competitor to be an investor? they'd have information and leverage you wouldn't want them to have), and it defeats the purpose of a break-up fee (Figma negotiated for it because they didn't want to spend a year of their lives focusing on something that would benefit their competitor if it's all for nothing... Adobe gained a year, has a ton of information, and distracted Figma).