Tarot is a tool for reflection, not for making decisions instead of you. The cards reflect what's already going through your head and help you see the situation from a new angle, but the choice remains yours. In your case, the question isn't about the cards, but about whether you're ready to sacrifice stability for growth and interest. That's a perfectly legitimate desire - boredom at work gradually eats away at your motivation and confidence, even if the salary is good.
Try evaluating the startup not through the cards, but through concrete factors: do you have enough of a financial cushion if the project doesn't work out? What skills will you gain there? Can you see yourself in this team in a year or two? If there are no prospects in the marketing department and even a salary raise won't shift the boredom, then a startup might be the push you need. But if you're risking your last money and don't see a plan B, that's not about the cards anymore - that's about common sense.
A reading might tell you to listen to your intuition or that it's time to act, but you make the actual decision yourself, based on facts. Sometimes it's better to move to a similar but smaller company than to jump into a startup. Sometimes a startup is exactly what you need. The cards don't know your financial situation and your ambitions.