One of the rules of the Thai Privilege Visa is that members are not permitted to work for a company located in Thailand. This is because a Thai work permit is required. 

This exact same rule also applies to setting up a business within Thailand. Holders of a Thai Privilege Visa cannot establish a business in Thailand or sell goods and services to their customers within the country.

However, if you are a holder of a Thai Privilege Visa, you can still set up a business provided you follow these following guidelines: 

• The holder of a Thai Privilege Visa can set up a business based directly in an overseas territory with the chance for them to work remotely for that establishment while living in Thailand.
• Thai Privilege Visa members can set up an online business and work while in Thailand as a digital nomad.
• The member of a Thai Privilege Visa can work remotely while in Thailand for that business and earn revenue/income from it.

If you fulfil those above conditions, you can establish a business via conventional means.