Neutral is common even if you have 3ph wiring.
Generally neutral is shared but you need to keep certain special purpose neutral as dedicated virgin, do not connect anything to them (special purpose = i.e. the Water Heater or wet floor SSO) which are connected to 10mA RCD.

10mA RCD is very sensitive and it will not be able to operate if there is imbalance caused by the injected return path (it is more sensitive than your finance department when you submit fake claims using next door workers' receipts - when you are only entitled for own-expenses claims)

When I performed house renovation, my electrician informed that I shouldn't pull the neutral from adjacent 13A plug point to the smart switch due to the separated circuit of the 3 phase system (light + fan for 1 phase, 13A points for 1 phase and others in another phase).
Hence, I only purchased no neutral smart switch.

Anyone can verify this?

Yes and yes. Simple to say all the RCD in your pic are the 0.01, 0.03, n 0.1 blocks with test buttons.

If the 3 phases all use the same rcd, no issue.

If they split them to 3 different rcd then can cause the rcd to trip if the neutral returns to a different phase rcd

Thanks bro, so basically I'm guessing the 0.01 for heater, 0.03 for 13A and 0.1 is probably for the fan/switches
So for my layout, even my upstairs looks pretty similar. Meaning I could just grab the neutral from other phase since it is going back to the same RCD? (except for the water heater I guess).

Does the neutral wire need to be in the same phase or even circuit for it to work?

Eg. lights on R1 while the switch I'm taking from is on Y5 for example. or I need to grab from R1 lights from R1 13A switches?

When I performed house renovation, my electrician informed that I shouldn't pull the neutral from adjacent 13A plug point to the smart switch due to the separated circuit of the 3 phase system (light + fan for 1 phase, 13A points for 1 phase and others in another phase).
Hence, I only purchased no neutral smart switch.

Anyone can verify this?

The phase to phase voltage is 415 volts AC. Phase to neutral or phase to earth is 240 volts AC.

Any Mitsubishi JP series (Mr Slim) users here? Do you appreciate having the ability to access the rollers directly?

I currently stay by the main road, using Panasonic inverter which uhh every 3-4 months I need to call people to come clean mainly cause the blower is clogged up.

Am surveying if I should stick to Panasonic or maybe move to Mitsubishi for my new home (mixture of wall and cassette wiring/piping provided by developer).

This is not aircon thread boss
Maybe should consider installing those DIY magnetic insect screen (if windows left open to filter out coarse dust bunnies) and Sharp air purifier/air filter.