It’s always awkward when ex-founders, ex-CEOs, etc. remain on the board, at least 90% of the time.
First, things will change. As you leave your operating role, the company will a year or two be very different from the company you worked out.
Second, the Board is the CEO’s boss. Having an ex-colleague as your boss is full of issues and micro-conflicts.
Third, it creates tension & distractions all around. Even if you don’t see it. This helps no one.
Step down and move on, and let the company make the most of your equity.
That’s where your return is.