When will Microsoft Drop IE? In 2025. Enjoy the countdown.
They have done many things to diminish support for it previous to that, including dropping it from their major web properties, such as Microsoft Teams and M365. But it won't fully go away until long after now.
The reason this is the case is complicated. IE11 is a part of the Windows operating system, unlike most browsers. Thus it’s tied to the OS lifecycle. When the version of Windows a user is on stops receiving updates, the IE11 on that computer will stop receiving updates as well.
For operating systems, Microsoft has had two support phases: mainstream and extended support phases. Mainstream phase includes all updates to the software. Extended support includes only security updates. The policy into the future, the one covering Windows 10, has changed that.
Microsoft has said that its Windows software is switching to a service model: “Windows will be delivered as a service bringing new innovations and updates in an ongoing manner, with continuous value for our consumer and business customers
This means that Windows 10 has essentially just one phase, mainstream support, because it's covered under Microsoft’s Modern Lifecycle Policy, where products are continuously updated and licensed. It does have a stated extended support end date in 2025 (And even some Long-term Servicing Channels for Windows 10 into 2029!). But how this will be resolved considering it’s the “last version of Windows” isn’t clear.
What does seem clear, however, is that Microsoft is supporting IE11 because it has to. They'll continue supporting it even after they stop supporting Legacy Edge.
It’s not actively developing IE11 -- it only gets security updates and technical support. In fact, it’s considering IE merely a “compatibility solution”, not a browser and definitely not modern. It is wrapped up in the OS lifecycle, and the company has made commitments. But the support of the browser is sure to be minimal from Microsoft since the company is clearly encouraging users who can to get off of IE and go to Edge.