lovefromisrael Have you tried to follow Proton Pass' official instructions?
(Edit: To others reading this: you don't have to do this if you're using Vanadium, as the necessary support is already enabled there).
Past posts in this forum on passkeys in Chromium-based browsers will be outdated, as Google are changing these "flags" not rarely, and Chromium's third-party passkey support is still experimental.