Mac storage basics · System Data and the storage categories
What is the Developer category in macOS Storage settings?
Short answer: It's data left by Xcode and its tools — build products, caches and indexes — which are rebuilt on the next build and can usually be deleted.
Developer appears when Xcode or its command-line tools have left data on your Mac — build products, caches, project indexes and similar. Its info button lets you delete some of it straight away; these files are rebuilt the next time you build.
Not everything developer-related lands in this category: simulators, device support files and container images are often counted under System Data instead. See freeing Xcode space.