The usual shapes
A handover period of three to twelve months. A part-time consultancy on specific accounts. A retained minority shareholding that you sell later. Or a chairman-style role with no day-to-day duties.
All of these are common and none of them requires you to keep doing the job you have grown tired of.
Be specific about what you keep
Most owners want to keep the customer relationships and the technical work, and hand over payroll, HR, compliance and the 11pm worrying.
Say that out loud early. A well-drafted role is a pleasure; an undefined one becomes a grievance within a quarter.
Who decides what
After completion the buyer owns the business, and being an employee somewhere you used to be the boss takes adjustment.
Agree in writing where your say is final, where it is advisory, and when the arrangement ends. Clarity here protects the friendship as much as the money.