Everything but a few proprietary, business focused modules in the backend (like managing multiple organisations) is AGPL licensed. Unless you’re a business, you can probably make do with just the open source code. They’ve even included a compile flag to disable all proprietary code. The clients are all GPL-licensed as far as I can tell.
You can also run Vaultwarden as the backend, which is a third party server that takes a lot less RAM but isn’t suitable for hosting thousands of active users at once. I also don’t think it has been audited, unlike the Bitwarden code. Great option if you trust them as much as you trust the Bitwarden company to maintain security.