Journal on Mac os?

There are No Apple Journal application in macOS 13 Ventura, macOS 14 Sonoma or macOS 15 Sequoia

As for " in development " ?

Asking us to speculate on what Apple's plan may be in the future ?

You are best direct that question directly to Apple as only they know what their plans maybe

 Product Feedback and ask Apple what their plans are for a Journal application for macOS

What does "journal" on macOS mean? If you mean something like a diary, there are already lots of third-party apps for that like Day One, in the App Store. Not sure Apple would develop a native app for that.

Although, you could always provide feedback and make a feature request if that is something you think they ought to consider.