Type 3: Light conversations with colleagues, exchanging ideas in a light-hearted manner. Can engage in this kind of work 8+ hours a day
Type 2: Programming a greenfield project, working in a familiar codebase, solving easy problems. Participating in low-effort meetings. 6-8 hours a day max.
Type 1: Challenging problems, non-obvious solutions, messy codebases. Engaging in difficult conversations, leading meetings. 4-6 hours a day max.
I've found that when I'm well-rested and in a positive mental state, these are my capacities each day. I can temporarily go over, but much like sleep, I need to catch up (by working less). If I exceed any limits, my productivity is reduced until I get some rest (e.g. by taking an easy day or engaging in lower-level work the next day).
Plus I have hobbies and friends and family that I want to spend time with. Life isn't about maximizing work productivity.