Is it allowed to return to Thailand with a 7-day immigration stamp after a visa run to Cambodia?

I suggest you get a tourist visa to return to Thailand from the Thai Embassy in Phnomn Penh.

You run risk of being denied entry on arrival in Thailand if you have a recent history of using various visas, visa exempt and COVID extensions to live in Thailand.

And as you will need to get a RT-PCR COVID test in Cambodia before flying to Thailand that takes at least two days to obtain results. There are only several authorized hospital clinics which can give you the COVID test and appointment is required.

To obtain the tourist visa or any visa from the Thai Embassy requires 3 business days.

I have placed the TOPIC ...CAMBODIA on your post. CLICK on it and all posts te CAMBODIA will pop up to read from others who have gone to Cambodia for a Thai Visa.

You will need a Thailand Pass to enter Thailand and meet its requirements.

You will need a RT-PCR COVID test within 72 hours of your departure from Thailand to Cambodia.

You must be FULLY VACCINATED to enter Cambodia.

You must obtain an EVisa online from Cambodia to fly to Cambodia. There is NO visa on arrival in Cambodia at this time.

And when you do return be prepared to answer questions from Thai Immigration on arrival

"Why do you stay so long in Thailand?"...

...And be able to show 20,000 Thai baht in CASH...if asked. NO ATM card or bank statement allowed.

...Have a confirmed air ticket departing Thailand at end of the entry or visa entered on...

...Have both booking of the Test N Go to show...

...Have your after Test N Go address to show.

...along with other Thailand Pass requirements including required health insurance.

Good Luck...