Container Queries and Subgrid are only available in Safari Technology Preview, not stable, and Firefox has actually been supporting Subgrid for more than 2 years. Because CQ is not supported by either Chrome of Firefox, it will be at least 2 years before we can start actually using it.

It would have been much wiser for Safari to catch up on the dozens of features they don't support that both Chrome and Firefox do, or to focus on bug fixes for the most basic features that's been broken for years. Instead, they chose to ship shiny new ones to try and convince both regulators (from the EU, UK, US, etc) and web developers that they are leading the way in feature adoption. Unfortunately this seems to be working to some extent in the web devs community. Regulators are unlikely to fall for it though.

Here is the 7 years old scrolling bug I'm referring to, which prevents any decent implementation of modals in Safari on iOS: https://github.com/web-platform-tests/interop-2022/issues/84

Here you can see that Safari has 5 times more API failures (representative of both missing features and bugs) than Chrome, and 3 times more than Firefox: https://wpt.fyi/