I installed the fdroid version (this was the motivation to do the backup) and I tried doing a backup from it. It works. So it must be something with the apk version.
Thank you for testing. I’m on LineageOS 16.0 (January 14), and I have 18 GB free. The “…%” part never shows, so I get it’s stuck before even starting to backup.
I guess you could try downgrading by re-installing an earlier apk, and then exporting a backup from the earlier version. But I’m not entirely sure that’s safe, and if it’s not really urgent, maybe better don’t^^
This happens to me frequently when I have the device connected to a WiFi network without Internet, maybe the problem, Delta tries to connect to the server before doing the backup,
I’ve put my phone in airplane mode and I see the same thing. I’m not sure this is the problem as the other instance of Delta Chat (installed using fdroid) was able to backup.
This happened to me when IMAP thread died because of a bug that is already fixed. Try putting the phone in airplane mode (as suggested above), reboot it and then initiate a backup
So I tried to create a backup for the desktop app (it fails: I am asked a location to save the backup, and nothing happens), but as I did it I saw that the Android Delta Chat had actually created some backups in my Downloads folder. I imported the last one and it worked (with one exception: the profile picture is not shown in the imported chat).
So I guess the issue is not that the backup is failing, but that the dialog to create it does not go away when it’s done.