Auk wrote: You need lower temperatures - so it drops its leaves and goes dormant.
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Auk; do we know where the OP is located?
Northern or Southern Hemisphere?

Anyway, if you are in the Northern Hemisphere (Winter now), forget about "lots of sunlight", Auk is right.
If you are in summer now, as I happen to be, then it needs as much sun and fresh air as it can get.

I am in Hong Kong, approaching winter. very very dry air now

pinkegg wrote: approaching winter. very very dry air now

im in the northern hemisphere as well and also approaching winter. if possible your tree needs to go outside, if thats not possible you need to place the tree somewhere that can best mimic it being outside. as Auk mentioned you need the lower temps (which i dont see how you can achieve that indoors) so the tree can go dormant as my maple stays outside 100% it is now starting to drop its leaves for the winter. i mad the same mistake years ago and kept a small maple (looked just like yours) indoors and it did not come back to life after winter.

If it is a Hong Kong species it might survive inside but if the species comes from Japan it might struggle. I don't recall seeing a single maple when we went to the bonsai nunnery in Kowloon, so it might be a struggle.

Good luck.

to raise the humidity arround your tree, you can have a "large and deep" tray, fill it with pebbles and water and put the tree on top of it, make sure the pot isn't in the water. Something like they do in Ginko bonsai center

very informative, thankyou all very much!

will try the water tray idea.

stupid idea, would it help if I keep it in the fridge overnight and bring it back out during day time for some sun? I keep it in a room without a heater but still I don't think I can lower the temperature much more.

Plants do not like to be moved around, and do not like swings in temperature. As such, moving it to a fridge for a few hours is not going to help. I know some people who keep temperate species in a fridge for a few months to give them winter, which brings a whole other suite of challenges.

Water trays for raising humidity.. have been debunked a looong time ago. Unless you are able to sends dozens of litres of water in the air, or enclose the tree