Keeping copies of the database as one goes through fix attempts (e.g. the repair you might run soon) is always good, but for SQLiteDatabaseBrowser use, I would hope that “Open Database Read Only” works.
Odd about the quotes. Mine accepts double quotes, but not two-in-a-row as one gets from source paste.
Duplicati puts many dup* files in tempdir, and its random names make it hard to tell what’s what without opening (try adding suffixes such as .zip or .aes. Sometimes it’s even SQLite database. Possibly this is significant, as active Duplicati temp files would possibly be locked intermittently. Locking was suspected in Locked files seems to cause corrupt backup #3594, where I’m pointing back here, and encouraging help.
That’s an open invitation to anybody, especially those on this thread. Finding a simple way to get it will be wonderful. Setting up higher levels of –log-file-log-level for –log-file may also help, if it’s random but likely. Logging can also help see if a prior locking error seems to be related, and might also be a workaround, if excluding areas giving issues is reasonable. Sometimes it’s not, but temporary files can likely be skipped. That’s coming at things the other way. One is how to make it, the other is how to avoid it. Both can help…