It's totally embassy dependant. Mine (Seoul, Korea) did demand real fully paid tickets. I sent them my one way ticket on Thai Airways and was approved.
it doesn't. Only F-2/F-4/F-5/F-6 visas grant residence status in Korea. This might not be relevant at all for Thai Embassy matters, but for Korea, you're not a resident as in long term resident. The F-1-D visa (yours) can't be extended beyond 2 years. The Thai Embassy in Korea might have changed the rules, but when I applied back in August 2024, only "residents" (F
***
/
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) were accepted for DTV applications. For other visas such as SETV or METV, the residency status didn't matter at all, even back then.