Never rely on any cloud service! A good cloud based password manager is end to end encrypted meaning the password manager provider cannot access your passwords and they are secured from the provider and any compromise of the provider. But you do not only need confidentiality but also reliability. The cloud is just someone else’s computer that you store your data on. They can cease their service or stop providing you access to it at any time. Always have a local backup of anything important saved in a cloud.
With Bitwarden for example you can export your vault as unencrypted json and csv format. Those are widely compatible and allow you to easily access and import your passwords.
Do not save your exported passwords unencrypted. I strongly recommend creating a dedicated VeraCrypt or LUKS container or similar and saving the export directly into that without saving it to disk unencrypted in the first place.
Note that shared organizations are not included in the standard vault export and need to be exported separately.
Edit: Someone mentioned that Bitwarden’s export feature does not export attachments. So export them manually if you need to.
If you are the BitWarden server admin, what do you see per user? Just a blob of data called “encrypted password database” or something, along with something like a last modified date and version number for syncing purposes?
The entries are individual DB entries, but fully encrypted, yes.
For organizations you also have encrypted keys in there, which can then - via asymmetric encryption - be shared by organization admins to new organization members. Still E2EE - the server is only the messenger/orchestrator here.
So the most an admin of a server sees is metadata (number of entries, how often they are modified, synced etc).
I think the only “plain” information on the server is the email address of the account itself … which you need to login with your bitwarden client and which can be used for sending notifications. The password for validation that you are who you say you are is client side derived from your master password. So the server cannot reverse it to your master password. It’s essentially also an asymmetric login information; you can produce the necessary information to prove to the server that you know the master password, but the server doesn’t know the master password. Cryptography is fascinating.