We keep encountering situations like this where a new chemical compound was introduced, becomes ubiquitous in our diets or environments and only later do we find out "Oops, it has serious health or environmental consequences."
It is worth the cost of slower introduction of new materials to take the time to ensure that those materials are safe. We're still paying the cost of introducing lead into our environment in a myriad of subtle ways. We still don't fully understand what the cost of the introduction of microplastics or PFAS is going to be. And regardless of the whether this particular study holds up under replication it is looking increasingly likely that aspartame is not something we should be consuming.
And what's most frustrating is that the people who profited most from these compounds never pay for the damage they cause to generations.
How can you ever prove something doesn't have any negative impacts? You're trying to prove a negative. Would you be willing to further delay a new medication that can help people today, but may have some averse effects for a subset of people far in the future? This is what we went through with the mRNA vaccines. We have to look at the tradeoffs. If banning aspartame means we may potentially prevent some cases of autism, but at the definite cost of large increases in obesity, would that be worth it?
Aspartame and added sugar would both be scrutinized in this hypothetical future where we are bit more cautious.
The answer is to probably ban aspartame if there is good reason to believe it is harming us, and/or tax sugary drinks until their negative externalities on society are paid for.