Is iOs 18 compatible with MacOs 12 and iPadOs 15?

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I have an iPhone XR that is prompting me to update to iOS 18. However, my MacbookPro can’t update past MacOs12. And my iPad can’t update past iPadOS 15.

If I update my iPhone to iOS 18 will everything still work with my Apple devices?

I am particularly concerned about iCloud passwords, as I know that in iOS 18, the password feature is now a standalone app.

I am also concerned about syncing Reminders lists and the Notes app.

I’d love to hear from someone who is using iOS 18 with other older Apple devices. Thanks!