In order to apply for a Thailand Business Visa you must fulfill one of the following requirements:
have a valid working permit
be Director of a company under BOI program
have an invitation from the Ministry of Labour
Furthermore, the traveller must have also an invitation letter from a Thai Registered Company and provide the documentation described in this article: http://www.siamdevelopment.com/covid-visa/how-to-get-thailand-business-visa-during-covid-new-normal/
Updated information on sanitary situation can be found here; https://ddc.moph.go.th/viralpneumonia/eng/index.php