Sync without deleting

First time sync
I synced Android Joplin with nextcloud (webdav)
Now I want to sync Debian Joplin with the same nextcloud. May this delete everything or perhaps something as I found happened, browsing the forum. Is there any risk? Should I take any provision before doing that? I tried to backup Android notes, but found no option to do that. I understand that only desktop Joplin is able to backup, so that only after sync I’ll be able to backup Android notes.
Joplin desktop 1.0.193
sync version 1
profile version 28