I went with a workaround as I seem to have reached the limitations of go templ. While injecting content into a rendered template is possible, I faced the issue, that when trying to reach .../item/:id without previously visiting .../items/ the other page contents are not being rendered.

So I stored the data that is being displayed in a session and extract it when redirecting and rendering the new page. That way the user does not notice the reload of the contents that should remain the same when redirecting as I can preload the data from the session storage into the template.