this is from travel-doc-aero (Thailand page) badly worded but applies to 1 day test & go.
The requirement to stay within any of the above countries for 21 days prior to departure does not apply to nationals and residents of Thailand, provided they travel from Thailand to an approved country and return within the last 21 days. These passengers must hold the following documents:
A Covid-19 vaccination certificate proving that at least 14 days have elapsed since the first dose of the Johnson and Johnson vaccine or the second dose of the AstraZeneca, Moderna, Pfizer-BioNTech, Sinopharm, Sinovac or Sputnik vaccine, or a Medical Certificate of Recovery for passengers who have recovered from Covid-19 no later than 3 months. Unvaccinated passengers aged 11 years and younger can enter provided accompanied by a vaccinated adult;
Covid-19 travel insurance certificate; and
Booking confirmation of a SHA++ Hotel booking and a required RT-PCR test at the hotel. Passengers must stay in their booked accommodation until receiving the test results within one day.
luckily not all airlines will use this information as gospel... I'm flying with Qatar on Sunday so just checked:
Effective 1 November,2021, travellers traveling under Test and Go scheme should provide a confirmed payment for a 1-night stay at SHA+, AQ, OQ, or AHQ accommodation, and 1 RT-PCR test.