is iphone 8 plus support bluetooth 5

iPhone 8 supports Bluetooth 5.0 --> iPhone 8 - Technical Specifications - Apple Support

That said, most earbuds are backward compatible with earlier Bluetooth versions, so they should work with an iPhone 8.

The iPhone 8 Plus is a 7 year old model that was discontinued 4 years ago; it does not support 5.3, it only supports 5.0.