I don’t get it, what does “a temporarily embarrassed founder” mean?

It’s a combination of “temporarily embarrassed future billionaire” with the (mostly mythical) “garage software business founder”.

Many software programmers (including me) spent the first decade of our careers sure we would produce a world-shaking program in our garage, and then found a company to scale it to the world.

It’s a reference to this quote:

“John Steinbeck once said that socialism never took root in America because the poor see themselves not as an exploited proletariat but as temporarily embarrassed millionaires.” ― Ronald Wright, A Short History of Progress (source)

Edit: apparently the original John Steinbeck quote was:

“I guess the trouble was that we didn’t have any self-admitted proletarians. Everyone was a temporarily embarrassed capitalist.”

“i would totally be a founder right now if it weren’t for [excuse xyz]”