1.If you want to share news include news in 23 sites associated with the hub site with external users, you must share hub site and all 23 site with external users. So prevent external users accessing public folders in 23 sites associated with the hub site is not available.
2.If you want to share news exclude news in 23 sites associated with the hub site with external users, you just need to share the hub site with external users.
3.Here're steps about how to share a site with external users.
(1)Enable external sharing in the tenant level. Go to SharePoint admin center -> Polices -> Sharing -> Set Anyone in the Content can be shared with section.
(2)Enable external sharing in the tenant site level. Go to SharePoint admin center -> Sites -> Active sites -> Select the site -> Sharing -> Set Anyone in the External shaing.
(3)Share a site.
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