Rails is best as an API only, that's where it shines for me like no other tool.

You’re overlooking Hotwire, PWA as a first-class concept, and Hotwire Native — the easiest way to take a functioning web app and migrate it to native mobile apps on both iOS and Android. I’d encourage you to take a fresh look at the new Rails technologies introduced in Rails 7 and Rails 8. You may find that the current Rails stack is the best fit for most, though not all, cloud applications that need a web client along with iOS and Android clients.