I had already discovered setuptexttexts myself. But how to do it 
‘nicely’ was still missing.

Thanks to Mikael and Wolfgang


Am 24.01.25 um 17:44 schrieb Wolfgang Schuster:
> \setuppagenumbering [alternative=doublesided]
>
> \setuptexttexts [margin]
>   [] 
> [\framed[frame=off,width=max,height=max,align={middle,lohi}]{\prefixedpagenumber}]
>
> [\framed[frame=off,width=max,height=max,align={middle,lohi}]{\prefixedpagenumber}] 
> []
>
> \starttext
> \dorecurse{100}{\samplefile{lorem}}
> \stoptext