Yes, its about Mounting + Editing, not just exploring or transferring.
For FTP, SFTP, and Samba https://github.com/zhanghai/MaterialFiles works perfectly.
For WebDAV, see this video https://youtu.be/FwfwNXFtvYE , It uses https://f-droid.org/en/packages/at.bitfire.davdroid/ along with Material Files.
