I have developed a version of an app than works when the device is offline, and syncs to a cloud server via the API. Works great I'm proud.
Time was (last year) I could broadcast new versions of the database through messages. Users would tap and choose to open in FileMaker Go.
Today, users can not tap to open in Messages? And iOS Mail say, "unrecognized file type" even though the user has Go 19 installed?
Does anyone else deploy like this? Have you seen these types of errors?
You can still do this. It's a few more steps than you used previously.
In the message thread, tap on the picture of the person who sent the message. That reveals a sub-menu. Tap on the info icon. That reveals a comprehensive display, including all documents sent by them. You can locate the file in the documents list and proceed as usual.
The how-to I learnt from is at How to Save Audio Attachments from Messages on iPhone & iPad
Boy, will anyone will know to do this, it’s a bit convoluted. 
The old way to access attachments in messages was:
You still have to perform those steps, but first perform three non-intuitive steps. They take you from the document you want to act on, to a list of documents, so you can possibly select the wrong one. So much better?
Seems to be the new definition of better these days 
I eventually came up with a simple HTML5 instruction page that included the now 5-6 step process to Download from a server, Locate the File, and OpenWith FileMaker Go.
The download and share arrows are confusing to users. (almost the same icon but one's Down and one's Up and in the very same location)