Maybe it does not HAVE TO have a beginning, just because it is expanding.
Imagine it was cut in half, then half again, then half over and over...
You can repeat that for infinity. If the original point of origin contained (literally) everything, then you can cut it in half to make half of everything forever.
That thought has actually occurred to me. There are lots of “modifications” to the Big Bang theory that may or may not be true. We don’t know everything.