@Natnicha **********
from my experience (and people around me), DTV approval isn’t really about the passport, but where you apply and how clear your personal case is
also important: not all Thai embassies accept third-country applicants. e.g. in Dubai they usually require an Emirates ID, so you can’t just fly there as a tourist and apply. in many European countries it’s similar. Hong Kong and China may also have restrictions
if the one is officially employed by a Russian company, meets all DTV criteria, and is physically in Moscow, applying in Moscow should be fine
but if the person is self-employed / freelance / working for a foreign or international company, Moscow can be tricky. The Thai Embassy there requires specific documents that only locally employed applicants can provide. in that case, most Russians choose to apply in nearby countries like Laos, Vietnam, Philippines, Indonesia, where the requirements are more flexible towards freelances and remote workers.
tldr it’s not about nationality, it's about the case. good luck!