@KarlF12 Sorry about that. I was working late night trouble-shooting. I just woke up and want to reply to your post… only to discover that the problem has miraculously vanished.
The problem appears to have been a transient network issue. I have literally done nothing to my server (based in Hong Kong) since my last post except sleep. Now via command ./occ app:install bookmarks works as expected and via GUI, I can now reach the nextcloud app store.
Perhaps Nextcloud needs a better/more mirror server(s) for Asia? I have had this error previously, this was the first time I posted about it.
Anyway, happy morning, problem “resolved” before coffee
(Yes, on the next occasion I will post the detailed error. My bad.)
@szaimen I am on 24.06… and the issue seems to have resolved itself… I am about to update to 24.08 now, just for maintenance upkeep. This seems like more of an app store network connectivity issue, more than anything else.