I buy iphone 14 Pro Max in Singapore Apple shop, can I install 2 nano-sim cards in my iphone?

Phone sold in Singapore support dual SIM via one physical SIM card and one e-SIM. See: Use Dual SIM on iPhone - Apple Support and Using Dual SIM with an eSIM - Apple Support

Only iPhones sold in China support two physical SIM cards. See: Using Dual SIM with two nano-SIM cards - Apple Support

See:

iPhone 14 and iPhone 14 Plus - Technical Specifications - Apple (SG)

It will take one nano SIM and one eSIM, not two nano SIMs.