I want to get support in Thailand, is warranty cover ?

This is a user-to-user forum. No one here cares what products you choose to buy. Although I will point out that Samsung has the same policy on warranty repairs.

You can ship the phone to a friend in Singapore, but you can’t ship directly to Apple in Singapore.

Here are the warranty terms that apply to iPhones purchased in Singapore. However, these particular terms are universal for all iPhones.

https://www.apple.com/legal/warranty/products/ios-warranty-rest-of-apac-english.html

IMPORTANT RESTRICTION FOR iPHONE, iPAD, APPLE TV AND HOMEPOD SERVICE.

Apple may restrict warranty service for iPhone, iPad, Apple TV and HomePod to the country where Apple or its Authorized Distributors originally sold the device.

Granted a lot of this has to do with the way that Apple handles service. Most major repairs are done as a swap for a service device, where by policy Apple generally only will replace with a functionally identical device. There are regulatory requirements for any device with a cellular modem as well as other requirements. Apple also might not actually allow any repairs be done by AASPs in some areas because of limited distribution of their calibration equipment (look up the Horizon Machine). In that case all “repair” would be done as an exchange for a service replacement. If they could actually replace the screen assembly in Thailand, it might be possible to get that repaired under warranty even if it was bought in Singapore.

In most cases the warranty is only valid in the country of purchase.