@Felicia ******
>actually I report every 60days
If I'm a betting man, what you're doing is getting a 60 day extension of stay based on unable to travel due to COVID-19, and paying 1,900 THB each time.
>When is the earliest I can go in for another covid extension of stay (visa/stamp) to immigration on 20 July stamp from immigration Mthani
As Tod said, IN THEORY, you should be able to get a 60 day extension of stay based on unable to travel due to COVID-19 when you have 45 days or less remaining on your existing stamp.