Open-source password manager that a non-technical partner will actually use? Password Managers

Whatever you pick, write the recovery story down before you need it. Where is the master password if you are hit by a bus, who can get at the shared folder, and does the emergency access feature you are relying on require a paid tier. I have watched two families lock themselves out permanently and in both cases the software was fine and the plan was missing.

Bitwarden is the boring correct answer for exactly this pairing, because the clients are open source and the free tier is genuinely usable rather than crippled: unlimited passwords, unlimited devices, apps everywhere. If you want the extras, note that Premium went from USD 10 to USD 19.80 a year in January, and that the free tier lost integrated TOTP and file attachments in the same change, so check whether you were relying on those before you plan around the old numbers. For a household the family plan with a shared collection is the part that solves your actual problem.

KeePassXC on the desktop with a compatible iOS client and the database file synced by whatever cloud drive you already pay for. Fully open, no subscription, and the file is yours. I will be honest that this is the option your partner will abandon, because conflict resolution when two people edit the vault on two devices is a bad afternoon and there is no way to make it not be.

The thing that made it stick in my house was not the software, it was doing the migration for her in one sitting. I sat down with her laptop, imported the browser passwords, deleted the browser copies so autofill stopped competing, set up Face ID unlock, and walked through adding one new login together. Nine days is exactly how long it lasts if you hand someone an app and a good intention.

Open source matters less than exportability, in my experience. What you actually want is the ability to get a plain CSV or JSON of everything out at any time without asking anyone. Check that on the free tier of any candidate before you commit, because a couple of them make export deliberately awkward.