Every step below is from an official source
Switch from 1Password to Apple Passwords (iCloud Keychain)
What to do at 1Password before you leave, what Apple Passwords (iCloud Keychain) needs when you join, and everything else the switch touches. Your full plan is built in your browser and stays there.
Official sources reviewed . How we review sources
At 1Password, before you leave
Export from the 1Password desktop appBefore
On a Mac, open and unlock 1Password, select File > Export and choose the account. Pick 1PUX or CSV, then select Export Data.
How to export your data from the 1Password apps1Password Support. ReviewedExport passkeys from the iOS or Android appBefore
1Password says passkeys can only be exported in 1Password for iOS and Android at this time.
How to export your data from the 1Password apps1Password Support. ReviewedKnow what a CSV export leaves outBefore
A CSV export does not include security questions, linked items, linked apps or custom fields.
How to export your data from the 1Password apps1Password Support. ReviewedDelete the plaintext export file when doneAfter
Exported files are not encrypted and are stored in plaintext. Don't email them or store them online, and delete them when you are done.
How to export your data from the 1Password apps1Password Support. Reviewed
At Apple Passwords (iCloud Keychain), when you join
Import a CSV file into Passwords on MacDuring
Export your passwords from your old app as a CSV file. In the Passwords app, choose File > Import Passwords from File, choose the file, then click Import.
Import passwords from another app into Passwords on MacApple. ReviewedReview passwords that didn't importAfter
Imported passwords won't replace ones already in the Passwords app. You can review any passwords that couldn't be imported.
Import passwords from another app into Passwords on MacApple. ReviewedDelete the CSV file after importingAfter
When the import finishes, Apple's steps have you delete the CSV file to protect your accounts.
Import passwords from another app into Passwords on MacApple. Reviewed
Then: everything else the switch affects
The steps above are what 1Password and Apple Passwords (iCloud Keychain) say. Your full checklist adds the accounts, codes, payments and devices that depend on your password manager, in a safe order. It's built from your answers, in your browser.