Hello again!
Apologizes for the confusion, as you mentioned the engine and project were working, this is quite a peculiar issue. I believe the best approach would be a clear slate, not just uninstalling.
First, please delete the Cesium plugin manually by eliminating its folder, should be at either /Users/Shared/Epic Games/UE_5.xx/Engine/Plugins/Marketplace/ or /Engine/Plugins/
Next, clear the launcher’s cache, should be at ~/Library/Application Support/Epic/EpicGamesLauncher/Saved
Finally, fully clear the launcher from your system, reboot, and reinstall. For the full clear, delete the following folders:
- /Applications/Epic Games Launcher.app
- ~/Library/Application Support/Epic/
- ~/Library/Logs/EpicGamesLauncher/
- ~/Library/Preferences/com.epicgames.EpicGamesLauncher.plist
After the reinstall, try to open the launcher and your project without Cesium first. If everything works fine, test by adding the plugin manually only, from the plugin folder.