I am using Android version joplin-2.14.8.apk downloaded and pushed into my Pixel 6 via adb this morning.

Desktop App is 2.14.16 (prod, win32) also installed this morning.

I created two test notes. One in the Desktop app with a screen shot of a Putty window. And one in the mobile App, taking a picture of an envelope.

I am syncing both to my Webdav server.

For the Desktop, searching for a unique string only in the screenshot returned the pointer to the note immediately.
Once the mobile app synced and the Desktop app synced, I was also able to search for a unique string on the envelope picture and get the result back.

Trying both searches on the mobile app does not return a result. Searching for regular text in the notes does return the notes. So the mobile is able to do some searching.

The only areas I have changed in the mobile configuration are to enable sync, change the time/date format to US English standards, and clicking the Seach Index fix button in Tools.