First of all thank you for your application.
I use Joplin on both my computer (archlinux) and my phone (Android 9 and Xiaomi MIUI 10.3).
Everything works perfectly on my computer but here is a short list of the problems encountered during the installation on my phone:
After my first synchronisation none of the old notes available on my computer appeared. I had to make a minor change in each of them (creating a new version) for them to be synchronized.
After what the notebooks in which these notes are collected are not created. If they were previously created, synchronized notes are not attached. This only applies to new versions of old notes and does not apply to new ones.
If I create on the phone a notebook with the same name as an existing notebook on the computer and then transfer a note in it, the new notebook is also created on the computer (which causes two notebooks of the same name)
The images inserted in a note are not displayed, notwithstanding that the note was edited on the phone or on the computer. By cons they appear correctly on the computer whatever the origin. (See screenshots below)