Proton Pass is currently one of the only major password managers that does not support Apple's FIDO Alliance-based passkey import/export standard introduced in iOS/macOS 26.
Bitwarden, 1Password, and Dashlane all support it. This means users cannot export their passkeys from those apps into Proton Pass on iOS or macOS. It's a hard blocker for anyone trying to migrate to Proton Pass.
What needs to happen:
Apple published two APIs for this specifically for third-party credential managers:

ASCredentialExportManager — to export passkeys from Proton Pass
ASCredentialProviderViewController — to import passkeys from other managers

Both need to be implemented. The underlying format is the FIDO Alliance Credential Exchange schema, which is what makes cross-manager transfers work.
Until Proton Pass supports this, it's effectively incompatible with the passkey ecosystem that the rest of the industry has already adopted. For a manager built around user ownership of data, this is a significant gap.
References:

https://fidoalliance.org/mobileidworld-apple-introduces-cross-platform-passkey-import-export-features-across-operating-systems/
https://mobileidworld.com/apple-introduces-cross-platform-passkey-import-export-features-across-operating-systems/
https://developer.apple.com/videos/play/wwdc2025/279/