Why the lamp says it is unavailable
A smart bulb has electronics inside it that receive commands. Turn off its power at the wall and those electronics stop listening. The app may report the lamp as unavailable even though nothing is broken.
Leaving the switch on lets the bulb respond to schedules, voice or an app. But it also creates an everyday problem: the familiar wall switch can now disable the system. A guest using the room normally should not have to know that.
There are two broad approaches to consider. Keep the bulb powered and provide a compatible control that sends commands, or use an appropriate smart control for conventional fittings. Compatibility and installation requirements decide which is suitable. The important part is preserving a straightforward way to operate the light.
A reachable bulb still needs a usable room
A note asking everyone not to touch the switch is a fragile answer. It shifts the system’s needs onto the people using the room.
Choose a deliberate control arrangement
Compatible wall controls can send commands while the lighting remains powered. The right arrangement depends on the products and installation. Any fixed wiring changes belong with a licensed electrician.
I also check recovery after a power interruption and what still works if the controller is unavailable. Those behaviours are product-specific and should be tested.
Use smart sources where they help
Colour control, tunable light or a particular retrofit may justify smart lamps. In another room, conventional lamps with an appropriate control system may be easier to maintain.
When choosing, include replacement in the conversation. Can a failed lamp be replaced with a readily available equivalent? Does the new lamp need to be paired and added to scenes? Who has the account? Those are manageable jobs when they are planned for, but they should not be a surprise attached to changing a bulb.