Bootstrap, still the most popular CSS framework, officially dropped support for IE with the release of Bootstrap 5. Tailwind, another popular CSS library, also dropped support for IE11 with the release of version 2.
Many of Microsoft's own products have already dropped support: Microsoft Teams web app ended support in November 2020. From August 17th, 2021, Microsoft 365 apps and services will also drop support.
It is now Safari that is the major outlier. Few users are stuck on old versions of Chrome or Firefox, but plenty of users get stuck on old versions of iOS.