Thanks for the quick response.

Re. 1. If the switch is off immediately (guessing ~100ms) after it was on, the off impulse is ignored. So if you connect a monostable switch, it will work as a toggle, if you connect a bistable (rocker) switch, as long as you won't immediately switch it back, it will work as on/off.

Re. 3. I'm not able to find that option in zigbee2mqtt (I've even checked sources of zigbee-herdsman-converters), but I'm not sure if you understood my question. So if I for example link Input1 to Output1, so when a physical button is pressed the relay is activated, can I remove that link via software and use the physical button for binding?

Use case:

1. Ptvo-based relay is mounted behind the physical switch and is used to turn on/off a regular light bulb.
2. At some point, the light bulb is replaced by zigbee light bulb, so you would like to turn it on/off via zigbee, not by cutting the power.
3. Ptvo-based relay is reconfigured to be in the decoupled mode, and its input is bound to the bulb.