Can I get a DTV visa for attending a one-day cooking class in Thailand?

Only approved cooking classes, not just any cooking class.

I think all this is going to be tightened up over time and there will be one universal standard across all Embassies based on the strictest now. It won’t be easy.

Cooking class might not be the easiest. For some embassies, only a proof of a random medical appointment can make the deal:

No one can tell you with certainty as all Embassies seem to abide by different rules , but why would you need a 5 year visa for a one day course ?

Doubtful that an embassy will accept a 1 day cooking class to give you a 5 year visa. Each embassy sets their own requirements. There have been reports of embassies accepting multiple week classes, some accepting 1-6 months of classes, and some requiring at least 6 months of classes.

There have also been reports of schools claiming they are "DTV approved" which is a blatant lie because each embassy decides what qualifies and what doesn't, not the school. One person even made a post about their embassy rejecting their DTV application when they applied based on a school that claimed to be "DTV approved"