Quick answer: Construct 3 Photon spectator clients broadcasting their input events? Default subscription; spectators should be silent - check before send.
Spectator's inputs (cursor moves) broadcast to all clients; bandwidth doubles.
Guard broadcasts
if isSpectator: returnSpectators don't broadcast input.
Or per-role action sets
Spectator role has no input actions registered. Structurally prevented.
Audit role-based actions
Each action: which roles can broadcast.
“Roles in multiplayer are explicit. Spectator role needs to be considered.”
If your game has spectator mode, the per-role action map is mandatory.