A. Nony Mous wrong, 1 url for all online evisa applications, when you choose current location the submission is directed to the embassy with jurisdiction over that area. thaievisa.go.th
if the time is up, since you left Thailand you can try an entry. Definitely have all the bases covered, 20,000 baht or equivalent currency in cash, a ticket out within the time you'd be stamped in for, and booked accommodation for a week or more. Come in with a visa.
a visa simply is a document stating the reason you are entering, it's good for X days permission to stay in the country, it's used up upon entry (unless it's multiple entry). To stay longer you apply for an EXTENSION of stay. From that time onward you are on an extension of your permission to stay, the reason being whatever the visa was, such as retirement. Terminology is important because different rules apply to being on a visa permission to stay stamp or on an extension permission to stay stamp. Your stamp says PERMISSION TO STAY UNTIL. It doesn't say visa until, or retirement until.
Apply under workcation category. A contract and employment certificate stating you can work remotely and specifically in Thailand. Create a brief cover letter explaining exactly what you do, how you do it remotely, and why you want to do it in Thailand. Be prepared to show you have experience in the field of work with portfolio and banking proof that you've had income in as well. There isn't any real income needed, but there is likely banking proof of showing you have been getting income. Join Destination Thailand Visa (DTV) use group search and review similar success stories from your intended embassy
you can apply for an extension 30 days before your stamp expires at most offices, you don't lose any time, it's added onto your current permission to stay stamp