A new version of Studio will be released soon which will have breaking changes, that means older versions of plugins are not compatible with Studio 2019. In older versions of the plugins manifest file needs to be updated with maxvalue attribute. Adding that attribute will prevent user to install an older version to Studio 2019.
Without maxversion attribute:
With maxversion attribute:
There are few steps you need to do make your plugin to support maxversion attribute:
Search for <PluginDeploymentPath> and change 15 with (14 if you are updating a 2017 plugin or 12 if you are updating a 2015 plugin)
Original: <PluginDeploymentPath>$(AppData)\SDL\SDL Trados Studio\15\Plugins</PluginDeploymentPath>
Updated : <PluginDeploymentPath>$(AppData)\SDL\SDL Trados Studio\14\Plugins</PluginDeploymentPath>
Right click -> Reload solution -> Rebuild solution.
To test if plugin is updated correctly :
If after rebuilding the solution you receive an error regarding "PluginDeploymentPath":
Please unload the solution -> open .csproj and make sure you don't have any references to Sdl.Core.PluginFramework.build besides the one you just downloaded from Nuget which points to 15.0.2 version: