What actually matters when partnering up with a non-technical co-founder?

Building my second startup (I'm the tech person) - but solo this time after leaving my previous one due to disagreements with my co-founder(s) after 4 years. But I'm starting to feel overwhelmed juggling all the business stuff while building the product. What ended up mattering the most in your experience? What do you wish you knew before partnering up? And how did you figure out if you're truly compatible before making things official?