I'm sort-of supporting IE11 at my current company and it's not about the features, IE11 is full of rendering bugs & quicks which make you work more. Lots of CSS bugs, lots of JS bugs, it's just an outdated browser which has a real cost to support.
Then you need to be careful to include enough polyfills because even what you assume would be there probably isn't, there's no Promises, no Array.prototype.includes, no arrow functions.