Your result
Not eligible
There is no Thai descent claim here, and there is no second version of this route to try.
Thailand's descent rule is section 7(1) of the Nationality Act, and it is a single rule: a person born of a Thai father or a Thai mother is Thai. It runs from parent to child, with no generational limit, but it has to start somewhere. Thailand has no ancestry visa, no diaspora or heritage route, and nothing for people of Thai descent that sits outside section 7. So without a Thai parent, or a Thai ancestor whose line reaches you unbroken through your parent, the descent route is closed.
What is actually open. If you are married to a Thai citizen, that is a real route and a much shorter one than most people expect - it does not require permanent residence first. If you want to live and work in Thailand, employment on a work permit can lead to permanent residence after three continuous years, and permanent residence held for five years is what opens naturalisation. If you want to be in Thailand without that, there are long-stay routes for remote workers, for people over fifty, and for investors, and it is worth being clear that those let you stay without leading to a Thai passport.
One case that does not look like descent but is worth naming. If you were born in Thailand to non-Thai parents, you may be affected by the 1972 revocation of nationality from children born in Thailand to certain migrant parents, and by the provisions that have since reversed it - which depend on having been born in Thailand and lived there since, not on ancestry. If that is your situation, look at it separately; it is a different question from this one and the answer can be yes.