No, it's absolute ... there's no way to determine otherwise.

The thing about the solipsistic standpoint is that it is not merely the result of abstract phiolosophising but the product of biological reality — the irony of the external universe having a sui generis existence is that, if we are right about its nature then the fundamental truth of it is that we can have no way of knowing that to be the case (Descartes, Goeddel and Heisenberg were right).

But real insight that stems from the absolute truth of there being no way to determine whether any of it is real beyond ourselves is the realisation that attempting to define 'real' that way is based upon a failure to grasp the very nature of Reality ...

https://whereangelsfeartotread.medium.com/mental-masturbation-fba1482fd4b7