In MacOS Sonoma you can convert webpages to "native" apps using Safari's File -> Add to Dock... menu option. This creates an icon in the Dock and an app in the ~/Applications folder.
Overall very similar to the iOS, Share -> Add to home screen.
However, even when put into fullscreen, the "app" is not truly fullscreen. MacOS adds a top bar that is not part of the page. The screenshot below was taken on MacOS Sonoma with the test app in fullscreen. The top dashed red box is not part of my webpage. Usually Mac apps in fullscreen do not show their top bar unless the cursor is moved to the screen top.
A highly similar issue existed for iOS on Safari, and has been resolved. By placing meta tags in the page header you can to advise the "app" to take up all actual fullscreen, undecorated. (This only takes effect once converted to a shortcut homescreen "app".) For iOS, these are the header tags to ensure fullscreen:
<!-- Page meta, webapp iOS support-->
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="viewport"
content="viewport-fit=cover, target-densitydpi=device-dpi, width=device-width, user-scalable=no, maximum-scale=1, minimum-scale=1"/>
<link rel="apple-touch-icon" sizes="180x180" href="webui/icons/apple-touch-icon.png">
<link rel="icon" type="image/png" sizes="32x32" href="webui/icons/favicon-32x32.png">
<link rel="icon" type="image/png" sizes="16x16" href="webui/icons/favicon-16x16.png">
<link rel="manifest" href="manifest.json">
<meta name="apple-mobile-web-app-title" content="...">
<meta name="apple-mobile-web-app-status-bar-style" content="black-translucent"/>
<meta charset="utf-8">
I am looking for the tag equivalent for MacOS Safari File -> ... Add to Dock apps.
Are there tags to add to the header to get rid of the indicated top bar, which is not actual part of the webapp ?