I’ve found Joplin to be “acceptable” to share notes from mobile. When sharing through a shared drive, it saves each note as a separate markdown file, so it technically is greppable plain text, my only gripe is it puts all the files in a single dir. I think it can also import them, or you could add notes directly to the dir.
Over time, I’ve migrated most of my KB to some sort of markdown: Zim Wiki, DokuWiki, Joplin.
I still have some locked up in MediaWiki dumps, probably should spin one up and migrate it all.