https://gohugo.io/templates/introduction/#the-dot
https://gohugo.io/functions/with/
with
Rebinds the context (
.) within its scope…
Inside of the with structure, .Site.Title is non-existent.
{{ $foo := .Site.Title }}
{{ with .OutputFormats.Get "RSS" }}
<link href="{{ .RelPermalink }}" rel="alternate" type="application/rss+xml" title="{{ $foo }}" />
<link href="{{ .RelPermalink }}" rel="feed" type="application/rss+xml" title="{{ $foo }}" />
{{ end }}