fianlly it works

hugo.toml

@@ -3,26 +3,23 @@ languageCode = 'en-us'
 title = 'IRS Satellite Division Software Projects'
 theme = "minimal-theme"
 
-[[menus.main]]
+[menu]
+[[menu.main]]
 name = 'Home'
 pageRef = '/'
 weight = 10
 
-[[menus.main]]
+[[menu.main]]
 name = 'Contact'
 pageRef = 'contact'
 weight = 20
 
-
-# [[menus.sidebar]]
-# name = 'FSFW'
-# pageRef = 'fsfw'
-#weight = 10
-
-# [[menus.sidebar]]
-# name = 'sat-rs'
-# pageRef = 'sat-rs'
-# weight = 20
+[[menu.main]]
+name = 'IRS Website'
+url = 'https://www.irs.uni-stuttgart.de/'
+weight = 30
+[menu.main.params]
+blankTarget = true
 
 [module]
 [[module.mounts]]

layouts/partials/header/brand.html

@@ -1,4 +1,4 @@
-<a class="navbar-brand" href="https://www.irs.uni-stuttgart.de/" target="_blank">
+<a class="navbar-brand" href="/">
   {{ $image := resources.Get "images/unilogo_schriftzug_white.png" }}
   <img src="{{ $image.RelPermalink }}" width=200 height=auto>
 </a>

themes/minimal-theme/layouts/partials/menu.html

@@ -39,6 +39,9 @@ Renders a menu for the given menu ID.
     {{- else if $page.HasMenuCurrent .Menu .}}
       {{- $attrs = merge $attrs (dict "class" "ancestor" "aria-current" "true") }}
     {{- end }}
+    {{- with .Params.blankTarget }}
+      {{- $attrs = merge $attrs (dict "target" "_blank") }}
+    {{- end }}
     <li class="nav-item">
       <a class="nav-link" aria-current="page"
         {{- range $k, $v := $attrs }}