Opinion are not facts. Even if they seem so.
In response to the original question, chances are highly unlikely you would be asked to show 20,000 Baht. However, Thailand put that “rule” on the books over ten years ago. It was designed more for expats using the 30 day visa to stay in country. However they could easily start enforcing it again, if they so desire. My opinion -- they would like to, if their economy was better, so. Why not keep a stash of 700 Euros or dollars as a backup just in case? I usually do this on general principles while traveling.
A long time ago now, back in 2005-2007 Thailand would occasionally check. I was asked and showed money on two different occasions. One was extending a 30 day visa, and the other was arriving in Thailand after a Myanmar trip, flight to Kengtung and then exiting to Thailand. Both were at the Mae Sai border crossing.
Today I doubt they would, by why take the chance?!