Please check versioning on your plugin. Says that 0.5.0.0 is installed and the latest is 0.5.1. I have tried multiple times and it never removes from the list of plugins that need to be upgraded. I have seen this and experienced with my own connector. There is a mismatch between versions in the connector, nuget and app assembly.
Author: Alex ShlegaLatest version: 0.5.1Released on: 07/15/2020Nuget package Id: ItAintBoring.XrmToolBox.CanvasAppCodeReuseOpen Source: falseGo to project web site Ratings (all versions)2Average rating1Number of ratings Downloads1987Latest version2193All versions731.00Average per version