Hello, I had this same error. PHP was version 7.4.19, and WordPress 5.8. Neither recommendation above worked for me.
I was able to fix it by downgrading WordPress back to 5.7.2 (in the end, I’m not sure if this was necessary), and I commented out line 31
// include ‘include/lcp-widget.php’;
removing the include of the widget. And after that I could activate the plugin and it functions normally.
Thanks
