Angular 12.1 new features:
Improved CLI performanceng build defaults to prod, that avoids accident production deployment from development builds
New @use syntax points to new Saas API in Angular 12.1. Automatically happens when you do ng update on Angular 12.1
Angular components supports in line Saas in styles field in @component decorator
Strict mode can be enabled via CLI to catch errors early in development cycle
Webpack 5 module is Production ready
Unused methods will be removed to improve performance by DomAdaptor
Custom router outlet implementations are allowed
min max validators for forms are added
TypeScript 4.2 support has been added and dropped support for TypeScript 4.0 and 4.1
Deprecating support for IE11
Above some of the features, please go through official Angular docs for detailed info.