One thing I didn't know, a covid extension starts from the date you apply, not the date of visa expiry.
TLDR : Answer Summary
The COVID-19 extension in Thailand starts from the date of application rather than the expiry date of the current visa. Most immigration offices follow this rule, which means if you apply early, you lose the remaining days on your current visa stamp. However, if you've utilized previous extensions, the COVID extension may begin from the end of your last extension. It's recommended to check specific immigration office policies as they can vary.