Are there other platforms to invest in bank's share in US, China, Hong Kong & Singapore?

Other than MIP, you can use a regular brokerage platform to buy/sell shares in those markets.

Since you are targetting bank's shares in US/CN/HK/SG, these are well known names that will be avaliable in most brokerage platforms. Therefore, it will be down to who offers the cheapest comission fees across these few countries' stock exchanges. For this, I will recommend Interactive brokers or TD Ameritrade

For Singapore stocks, you can only use our local brokerages to buy.

For others, do consider Interactive Brokers. Yes, there is a minimum $10 USD activity fee/month but with the convenience, low fees & real time exchange rate and a one-stop consolidated portfolio tracker, I wouldn't mind paying for it.