Wait until Internxt have implemented WebDAV:
Internxt WebDav support | Internxt Help Center
At this time, we’re currently working on implementing WebDav support as well as other integrations. At the moment is not possible to integrate WebDav, FileZilla, WinSCP, or CyberDuck.
and then follow this Guide (Mount WebDAV-Resource with DAVFS2):
https://forum.sailfishos.org/t/guide-mount-nextcloud-webdav-folders-locally-with-davfs/8038