You need to install it by launching the installer.
Click the "Workload" tab* in the upper-left, then check top right ".NET-Desktop Development" and hit install. Note it may modify your installation size (bottom-right), and you can install other Workloads, but you must install ".NET-Desktop Development" at least.
*as seen in comments below, users were not able to achieve the equivalent using the "Individual Components" tab.
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