can you try what is marked solution in this thread? Access Murena Workspace from client apps on (old) iOS
I’ve also downloaded devx5, nextcloud and nextcloud notes.
/e/OS comes with a built-in davx5 fork (accountmanager), but there’s an interval for when files are downloaded/pulled (minimum 15 minutes atm). The nextcloud client should give you a “live” view of what is on the remote though.
Other methods would be a webdav mount through davx / accountmanager. Onlyoffice should be able to access this through the filepicker.