Can my STV visa be extended, and what are the current rules for Hong Kong residents regarding visas in Thailand?

Hello everyone,I want to ask again

I’m from Hong Kong ,my visa type is STV

I have few questions want to ask:

1:Rules said:visa on arrival have china,they include Hong Kong?

2:I ask few agents they said MY STV CAN EXTEND more 60 days ,so can I?have someone try already?

3:jomtien immigration new covid visa extend need proof documents now? Before didn’t need,so now new rules need documents?

Thank you everyone 🙏🏻🙏🏻🙏🏻🙏🏻😭