I'm newly arrived on Solus, after trying multiple Lunux distros in order to ditch Windows 10.
One missing item was replacing my current backup.
After some investigation, I found that Synology Cloud Station client runs happily on Solus 4.0 Fortitude (mine is with Budgie desktop)
To do this, with archive manager, I extracted the data.tar.gz from synology-cloud-station-backup-4450.x86_64.deb, and then copy the all files in it into the matching folders.
I can now successful configure and run a backup to a Synology NAS.
Still working on the Synology Assistant, as the synology-assistant_6.2-24922_i386.deb file I tried would not unpack properly with archive manager.