None of that makes Bitwarden not open source.
Yes, it does, because it violates its own license GPLv3 by having proprietary build-/runtime dependencies.
If it was under a different, maybe more permissive, open source license, then maybe it would still be open source, but as of right now i likely breaks its own license terms.
Not only that, they specifically state this is a bug which will be addressed.
From what they state, they think that because executables that share internal information via standard protocols does somehow not break GPL3 terms compared to two libraries that share internal state via the standardized C ABI which does. And they seem to not consider that a bug, just the build-time dependency.
So you meant to say:
That is not true, there are a lot of other password management software out there where the client source code is either open source or source available. For instance keyguard: https://github.com/AChep/keyguard-app?tab=License-1-ov-file#readme which is an alternative proprietary bitwarden client, where the source is also available. Also the Proton Pass client is under GPLv3.
I would argue that the main advantage of bitwarden compared to others is that it is open source and has an open source server for self-hosting (vaultwarden). Which of course makes it difficult in terms of business strategy with their VC funding. But maybe becoming a non-profit org and getting money from donors, the strategic funds of EU and other governments, etc. might be an alternative way.