Bitwarden uploads the whole vault (the whole json of passwords, passkey codes, MFA identifiers, credit card info...) encrypted with your master password. Meaning that whatever is on the cloud should be virtually unbreakable. That's why every time you write the password in the extension or Android app or whatever it takes a second or two to open, because it's downloading and decrypting everything locally.

When you update a password they need to reencrypt the whole vault and re-upload it again even though it's wasteful since that's their whole security plan.