Do Thai people need a passport for internal flights, for example, Bangkok to Chiang mai,  or is the ID card enough? When we flew to Phuket last time, they insisted on a passport but this was many years ago and maybe its changed since then.

The AOT site says ID card is sufficient https://www.airportthai.co.th/en/which-documents-are-accepted-for-domestic-travel❓/

 

ah okay, many thanks. 

Thai driving license also does the job, for Thais as well as foreigners.