Do you understand how computers work? You cannot do anything with data (e.g., display, edit, or autofill passwords) unless the data is available in memory for the CPU to access. The passwords are not stored in memory for frivolous reasons, they are stored in memory because the Bitwarden apps would not be able to function otherwise.
The best you can ask for is for a password manager to only decrypt vault items one at a time, as needed, instead of decrypting and storing the full contents of the vault. My understanding is that Bitwarden devs are working towards this goal, but this is going to require a major rewrite of large parts of the Bitwarden codebase (which consists of nearly a half-million lines of code, by the way), so it will take some time for that to be implemented.