Currently Bitwarden's passkey support is limited to the browser extensions not the apps but from my experience it works relatively well. When logging into a site you just select the passkey from the extension popup and it logs you in.

Example passkey registration:

• Click create a passkey button in the accounts settings page
• Bitwarden extension pops up with a list of matching accounts
• Select the account in your password manager that you want to associate the passkey with
• Click Save passkey button
• The account now has a new passkey associated with it that's stored in your Bitwarden vault

Example login:

• Click sign in with passkey button on the login page
• Bitwarden extension pops up with a list of matching accounts from your vault
• Select the account you want to sign in with
• Click Confirm button
• You're signed in