I can receive MMS including displayed pictures. Yet when I save them, without any error message, they are eventually just not present in Gallery. All of Chronology, Albums and videos are empty “Aucune photo, resp vidéo, trouvée” My provider is Free.
There are some open issues with MMS on different devices on Gitlab. You can check the issue and add your comments with logs or create a new issue.
There was no storage permission. Storage now works after I have enabled it for the message application. I was unaware of this setting and even less that I always got a feedback that file had been stored, without any failure feedback such as a kind of “storage permission not granted”.
Clue found by Marc Gonzalez on GITLAB. I had opened an issue in GITLAB and have added this comment too.