From Wikipedia:

Frank Oz, who previously performed as Bert, stated Bert and Ernie were not gay, saying,

"They're not, of course, a gay couple. But why that question? Does it really matter? Why the need to define people as only gay? There's much more to a human being than just straightness or gayness."[17][18]

Sesame Street went on to clarify further, stating:

"No, Bert and Ernie aren't gay - they're 'best friends'".[19]

The Gaystar News reported that fans reacted negatively to this assertion. Frank Oz later tweeted in September 2018

A last thought: If Jim and I had created Bert and Ernie as gay characters they would be inauthentic, coming from two straight men. However, I have now learned that many view them as representative of a loving gay relationship. And that's pretty wonderful. Thanks for helping me understand.[20][21]

So, I would say they weren't intended that way from the start but only because the writers didn't think to do so. Frank Oz is a great reference for these things, and if he says "I love how you see them as representation" then that's good enough for me.

No they weren’t.

They were created in the 60’s, the writer who head-cannoned they were gay wrote for them in the 80s.

Officially and historically they are not gay.