database disk image is malformed

Your database is corrupted, which generally happens from having your Zotero data directory in a cloud storage folder or network drive. You appear to have moved your data directory into the Documents folder, so if you're syncing Desktop & Documents via iCloud, you should immediately move it back to the default location. You should never store the data for any database-backed program in cloud storage.

You can try to fix the damage with the DB Repair Tool. If that doesn't work, and your data is all online, you can just delete the zotero.sqlite file (or move it somewhere temporarily for backup) with Zotero closed and then reopen Zotero and sync to pull down your library.

No, this is a custom data directory location. You would've had to have done this manually.

The default directory is just "Zotero" in your home directory, as explained on the data directory page I linked to above.

First, make a backup of all zotero.sqlite* files in your data directory.

Then close Zotero and move the Zotero directory back into the home directory so that it's at /Users/:username:/Zotero. When Zotero starts up, it will notice that the directory isn't at the custom location and offer to use the default.

You can then use the DB Repair Tool to try repair the database, or you can try swapping in one of the backup databases.