On Android, it's only accessible by the Manyverse app,
/data/data/se.manyver/files/.ssb
On iOS, it's an iOS-provided directory that only Manyverse can access.
On Windows, it's either:
C:\Documents and Settings\YOURUSERNAME\Application Data\manyverse- or
C:\Users\YOURUSERNAME\AppData\Roaming\manyverse - or
C:\ProgramData\manyverse
On macOS,
~/Library/Application Support/manyverse
On Linux,
~/.config/manyverse