Back in 2018, Google started testing a system for sharing content in Google Drive (including Docs, Sheets, Slides, and Sites) with folks that didn't have a Google account, by using a PIN-based verification system. Now called "visitor sharing," the feature is rolling out more widely to G Suite customers over the next month.
Usually, Google's beta tests don't take years to complete, but it makes sense that Google would give this feature as much time in the oven as possible. A lot of sensitive information is shared via G Suite, and a lot of big organizations depend on its functionality and security. Google had to make sure that the implementation for this system is both safe and reliable. Presumably, it passed the test over the last two years.
The feature is available in the Admin Console for rapid and scheduled release domains today, and will reach full availability for most G Suite customers starting September 28th. However, Google is not making the feature available to G Suite Basic, Cloud Identity customers, or normal Google accounts — that means most of us with @gmail.com addresses are out of luck.