Allow find usages in libraries without sources. Normally IntelliJ's find usages action does not include results from decompiled library sources. This plugin fixes that. Simply install and you're done!
Using IDE built-in plugin system:
Settings/Preferences > Plugins > Marketplace > Search for "Class File Indexer" > Install Plugin
Download the latest release and install it manually using Settings/Preferences > Plugins >
⚙️> Install plugin from disk...