Automatically activate installed plugins

"I already use the location described in the Lightroom SDK Guide on Page 31 (https://d1g4ig3mxc5xed.cloudfront.net/static/installers/lr/sdk/2019/doc/Lightroom%20SDK%208.3%20SDK%...), the Plugin is loaded an shown in the plugin manager, but it is not enabled/activated"

I just tested my LR 8.4.1 / Mac OS, and plugins in the Modules subfolder are automatically added to File > Plug-in Manager but are initially disabled.  I don't know of any way to automatically enable them.

If you manually place the plugin in the default folder for plugins, it should be enabled by default. 

Windows—C: \ Users \ [your username] \ AppData \ Roaming \ Adobe \ Lightroom \ Modules

Mac—Macintosh HD / Users / [your username] / Library / Application Support / Adobe / Lightroom / Modules