Is it somehow possible to make Home Assistant backups to cloud provider InterNXT?
Yes, but you may have to do it as a two step process, locally at first, and then move the backup files to the cloud as the second step.
I installed the HA integration rclone. Apparently you can make a backup to InterNXT with this integration.
Unfortunately I can't get rclone to connect with InterNXT. Haven't figured out yet why it doesn't work or will not connect to InterNXT.