https://github.com/Elsensee/phpbb-ext-posts-per-page
seems to me the tidier. Why this version is not in the DB, eludes my information.
Under phpBB-3.3.0-b1 I replaced before uploading the files parameters.yml, services.yml into the folder config for the version I´ve found on GitHub (!!) by: **)
parameters.yml, services.yml --> written here --> https://jsonformatter.org/yaml-formatter
**) Important: CDB extension database < || > Github - Because of different versions *) EXT-Version 1-1-1 from Github.
The extension of the *) mentioned version can be activated and used by me without error in the ACP under phpbb-3.3.0-b1 (PHP version: 7.3.11, system-version of the board: 3.3.0-b1)
Server: ErrorLogs have not been revealed so far.
BTW:
System: Maintenance work for beta versions are m.E. not essential but may be appropriate.
This can certainly only be judged by the developers. That is why my information is preliminary and without any guarantee. I do not have all tests yet. Everything seems to work, - can I first proceed in the form?
Will your extension undergo the following maintenance for upcoming phpBB releases? That would be great!

Best regards