OP, your question comes up often.
Some discussion here.
https://aseannow.com/topic/1318022-do-you-really-need-an-onward-flight/
You can buy a "rent a ticket" here is one of many companies
"onwardticket.com" approx $16 usd.
You can but cheapest throw away ticket approx 2k baht.
You can hope airline does not ask and if they do step away and use one of first 2 options.
Obviously you would need internet.