Here again, the problem is not a missing "=", it's invalid syntax somewhere before that.
Another thing we could consider doing here (and similarly for your original case) is
DETAIL: Expected "=" not "," after array dimensions.
The advantage of this is that it provides a little more clarity as to exactly where things went wrong.
One possibility all this ignores is that what we are calling array-dimensions are in reality most likely a user using json array syntax in our SQL arrays. That seems eminently more likely than someone mis-typing this niche incantation of building an array literal nowadays. I'd add a hint if the first symbol is [ and we fail to get to the point of actually seeing the equal sign or the first subsequent unquoted symbol is a comma instead of a colon.
