Keepass database with password and key file (which can be any file like a picture, or the MD5-hash of your pet’s name in a text file etc).
Put pwd database on favorite cloud storage ( in my case, NextCloud).
Do NOT put key file there (you copy that around manually and securely on a channel different from the cloud storage. Or even re-create it on the fly using the recipe you know like the pet-name-md5 example above.).
OwnKeyPass for SFOS, other keepass-compatible software on other machines.
Set up Sailsync on SFOS device, sync the folder with the keepass file .
Set up sync-on-change for the Sailfish-local place of the cloud storage. Set up additional systemd timer for syncing toward device.