To search in all extensions at once, use the standard search filtering by namespace
Where can I find a list of all existing extensions on one page?
Extension Matrix/AllExtensions is not up to date and "only" holds 2093 extensions.
Category:All extensions holds 2,383 extensions, but I can only see 200 at a time (I tried https://www.mediawiki.org/wiki/Category:All_extensions?limit=3000 but with no luck).
Why would you want to see all 2093 extensions in a single list? You can write a script to get all pages on a category using the API.
Actually, extensions are on their own namespace, You can use the standard search to do that, filtering by namespace!