What is the process for visa interviews in Thailand, and do all applicants need to attend one?

Well, you get notice a few days in advance ... so you have time to improve your parsa Thai.

/Sarcasm

You ask HOW it work?

You apply, Embassy sent an e-mail inviting you for an interview at day and time.

This can be done on-line OR in person at the Embassy, the Embassy decide which option.

You log in or show up at the Embassy on time and present your passport.

You answer all their qeustions.

I did my application in Manila in March and was asked to come in for an interview.

I was asked questions about my business (I applied for workcation) and what/why I wanted to be in Thailand.

They had asked me to bring my mobile banking accounts to show balances but did not ask to see them. They also told me I didn't have 3 months of the 500k balance so they would keep my application open until I could supply the final bank statement to meet that requirement (which was the March statement). I had to wait about 10 days for the March statement to be available and then they approved my DTV.

Not everyone, only those who get invited🤷‍♂️

Interviews are only if there is something strange in your application or you are from a high-risk country.

No, not everyone. Certain embassies do interviews for their application process, but it seems the majority don't from what I've seen posted. Hanoi, Vietnam did not when I got my DTV in Jan, but I'm sure someone has a list of the specific countries that do.