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Sorry for the confusion, the Graph view in 3.8 and previous versions only shows the curve between two keys based on what you select in the Dopesheet view. Therefore, when no key is selected in the Dopesheet view, it does not show any curve. The Graph view described on Graph - Spine User Guide is for 4.0 and later versions.
Another question. How to deinstall specific versions?, I see only install options in the launcher.
Open your user folder and delete the versions that you want to remove stored in the updates subfolder within it. Please refer to the troubleshooting page for user folder locations for each operating system:
Spine Troubleshooting: User files
