This is where your lack of understanding of the open source thing is readily apparent to everyone arguing with you. If it was backdoored, many people would be calling that out. In fact, this was one of the exact reasons at the heart of the original concerns leading to this story.
The fact that the source is available means that we can see exactly how the data is encrypted, allowing assurances to be made independently.
If nothing else, I trust Bitwarden MORE because of that and I'm happy to pay them for their services since it helps find further development.
If it was backdoored, many people would be calling that out.
In theory. And not necessarily soon.
Don't forget the context of this thread: we compare bitwarden with keepass, which does not offer to you your password base on their server side.
Dude, how is bitwarden hosting your own, locally encrypted (in FOSS client) password database any different than using keypass and syncing it however you want?
I don't even use Bitwarden myself, I'm using keepass too, but this attitude is ... weird?
I find risk slightly bigger when you encrypt your private data with the product of the company and store that encrypted data on servers of the same company.
Why: because if they have some backdoor now or plans to introduce it in future, they have all the time in the world to apply that backdoor to your data. Without you knowing it.
Bitwarden client is FOSS same as Keepass, though. Why aren't you afraid of Keepass having backdoor by "insert whatever big corporation sponsoring FOSS" giving said companies free access to your passwords you happily store in their clouds?