Firstly, open ArcGIS Pro, then click Settings. Navigate to Add-In Manager, then click the Options tab. In here check you have to folder listed, and than the option select is "Load all Add-Ins without restrictions (least secure)" (Note ArcGIS Pro does not support new signing methods, so in 2024 you cannot digitially sign addins).

Restart ArcGIS Pro. If it still doesn't load Discover, manually run the ArcGIS Pro Addin installer by double clicking on the file -

C:\Program Files\Datamine\DiscoverArcGIS\Datamine.Discover.ArcGISPro.AddIn.esriAddinX