It depends on your template.
I think by default, this is:
Pagename or Heading + tagline
I got the same problem and ended up adding a meta field in my collection of plugin.
https://combostrap.com/page/page-title-set-by-combostrap-72dytnms
The easy part would be to find a template that supports it or customise your template.
It would be great to have this functionality by default in dokuwiki but yeah…
