Can I stack my 30-day TR visa extension with the COVID 60-day extension in Thailand?

The COVID 60-day extension is likely to start immediately upon approval, rather than adding to your remaining days on your current visa. It's important to check if the office where you apply requires you to first take the 30-day TR extension, as some may insist on that. If approved without the 30-day extension, the COVID extension will likely be dated from the application date. Some offices may issue an under consideration stamp and ask you to return after a number of days to conclude the extension process.