KiMaN it's true Nextcloud use a database, but the directory exists in INSTALLDIR/DATA/%USER%/
Then you can view all the user data with Files app, by pointing config option root to the data dir:
'root' => 'INSTALLDIR/DATA/%USER%',
The Files app installation can be installed anywhere on the same server, and you just need to point root
to the nextCloud dir you want to view, using either relative path or absolute path.
KiMaN I want to use Files gallery to view Nextcloud structure.
I'm not quite sure how Nextcloud structures it's data ... If it uses folders, then of course you would also see the same folder structure from Files gallery menu. If it uses database, the structure is "virtual" of course and cannot be replicated by Files gallery, but you will still find the files.