From the Web.dev blog:
For the first time ever, all major browser vendors, and other stakeholders, have come together to solve the top browsers compatibility issues identified by web developers. Interop 2022 will improve the experience of developing for the web in 15 key areas. In this article, find out how we got here, what the project focuses on, how success will be measured, and how you can track progress.
You can check out the page here to see how the major browser engines are stacking up, and I've screenshotted the results for posterity.
As you may expect, Safari is well behind the other major engines, but the story does get much better when you compare the preview versions of each engine.
You can dig into what each browser does and doesn't support, if you'd like, too.
I don't think this is a magic bullet that will make it so developers can use the same stuff everywhere and just know it will work, but what encourages me about this is that the major players seem to have an agreement on what ought to be added in 2022, which is good for everyone.