Timelessness is completely different from infinite time.

When trying to understand how events took place before spacetime, timelessness rather than eternal time must be understood. Time does not extend back and forward infinitely. Timelessness means all events are superimposed into a single "moment" which is not really a moment.

Spacetime is just an organizing of the superimposed moments into a linear reel as opposed to a singular "moment" which is itself 0 seconds long.

Things happened before the big bang and spacetime, but the moments were simply not laid out in a row. They occupied the same precise position.