Do I need to prove 500,000 baht after leaving and re-entering Thailand on a DTV visa?

The 500k baht is a visa application condition, not an ongoing requirement. Read my post on this page mate, explains everything you need to know with the official sources. If you have any further questions ask in the comments mate

it is not beeing asked.

Myanmar is closed for border bounces. If you’re in the north, go to Chiang Khong and enter the Laos land border there.

There is no requirement to maintain funds on DTV, why do people think this ? , I really don't get it

Border run to Myanmar from Ranong has been done by some people successfully and you can find their posts in this group. Apparently, you take a boat, pay both sides of the immigration and be back on the same day without actually having to go beyond the Burmese immigration on the other side.

One post said they had to show business ownership papers (according to their original DTV application, I guess) but not the 500K fund proof.

For the other land borders with Myanmar (especially Mae Sot - Myawaddy), I don't think it's advisable to do a visa run.

Don't need to proof the 500k, and leave an entry anywhere you feel fit as it's a valid visa

As you are 90 days inside Thailand you need to make a 90 day report at your local immigration Office.

Next to that you need, if you drive a car or motorbike, a Thai driving license.

BUT, you can leave and come back to get a new 190 day period of stay as long as your multiple entry DTV is valid.

I leave and re-enter Thailand frequently on DTV.. Never once been asked to show anything on re-entry yet.

None.. There is not a single case of anyone being refused entry for not maintaining the balance, it is not a requirement.

People may be asked questions, that's totally normal (I don't understand why people freak out about it so much), but no one has ever been turned away.