Are there any Covid restrictions or vaccination proof required to leave and re-enter Thailand now?

There's no way one could be forced to show proof of vaccination to leave a country. That's a violation of human rights and as a foreigner you have the right to leave a country and go back to your own, without being required or compelled to undergo a medical procedure.

To enter a foreign country as a foreign national is a different story, there is no automatic right for non-citizens to enter.

Anyway, the whole Covid charade is over, except for a couple of countries in the region and central/southern Asia, including Indonesia, Myanmar, Philippines, Turkmenistan and Pakistan as well as a couple of Pacific Island nations.