Aspartame has been in common usage as a sugar alternative for literally decades.
If it was harmful or potent enough to be dangerous on a public or individual health risk then we would have certainly known about it by now. At this stage, even WHO, are saying it’s needed in HUGE concentrations.
Diet sodas aren’t the only things that we consume that contains aspartame. And aspartame isn’t the only thing we’re exposed to that has been linked to cancer and other deseases.
Just get on with life, enjoy what you enjoy in moderation. Don’t put too much thought into it otherwise you’ll just end up living in fear and avoiding everything.