Updated 12192023-150148
At initial release of iOS 17, there is a "Coming Later this year" button on Journal's subheading in the primary iOS 17 features landing page.
https://ax5u.short.gy/17journal
While it is possible to highlight text to format it to bold, italic, or underlined, it is impossible to manually insert a link. If you paste a URL, it cannot be tapped to open in Safari. The only way to open a link is to select it, swipe horizontally on the actions tooltip, and then tap 'Open link.' You can, however, add a link to a Journal entry from Safari via the share sheet, but doing so will create an entirely new standalone entry with a rich link, with no way of appending it to an existing one.
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