How roommates can share one good desk chair schedule
Start with each person’s fixed calls and longest work blocks. Reserve the chair for those periods, then rotate the remaining time. A shared calendar is enough; no elaborate booking system is needed.
Improve the backup chair with a cushion, footrest, or screen riser so the arrangement is not miserable for one person. Decide who maintains the chair and whether it is a shared purchase.
If both people need it daily, the real answer may be a second decent chair. Scheduling has limits.