Can I exit to Cambodia and return to Thailand on a tourist visa using the online arrival visa process?

You need to cancel your work permit and Visa extension. then you can exit the country there is no online visa for you unless you go to a Thai embassy You do have to fill in the TDAC form for arrival back in Thailand. Depending on your passport nation you may be eligible for a visa exempt entry stamp 60 days. Do not use the Poipet crossing.

Are you actually on a 90-day non-B visa or are you on an extension of stay? If you're on the visa, you can just leave and return visa exempt if your passport qualifies for that. You won't be returning with a tourist visa unless you apply for and pay for one from a Thai embassy while you're out of Thailand.

If you're on a work extension (the stamp in your passport says extension of stay) then you need to get paperwork from your employer that states your last day of work and take that to cancel your work permit and then your work extension. You can do this 1-2 weeks ahead of time in most places. If you fail to do this then you're not abiding by the documents you signed stating you would notify immigration of any change in your status. That means you won't be able to get another long-term visa or extension in the future until you do cancel your work extension, and you'll be fined 500 baht per day up to a maximum of 20,000 baht when you go to cancel for failing to do so on time.