I started on the forum: https://discourse.gohugo.io/t/can-splat-be-used-in-hugo-server-redirects-config/28292
Found out it is not possible to use a 'splat' variable to append the remaining part of the URL in a redirect.

It would be nice to have similar functionality in the server redirect feature as I use for Netlify redirects.
https://docs.netlify.com/routing/redirects/redirect-options/#splats