Hi there,
As you set your Blog page using The Grid you should not assign that page to Settings > Reading > Posts Page as doing that overrides the whole process and uses the default archive template of the theme.
So leave that page alone and consider it as your blog page and set the posts page to nothing in Settings > Reading.
Now for that page which you used The Grid, you can create a Sidebar and assign it to that page. For more information:
Then you can go to Appearance > Widgets and assign whatever widget you like to that sidebar which will show in the page with The Grid.
For the single posts, you can use simply the Main Sidebar widget area in the Appearance > Widgets menu.
Finally, to add a specific sidebar to your custom post types you need to install a Child Theme and add the PHP code below to the functions.php file of your Child Theme:
add_filter( 'ups_sidebar', 'portfolio_sidebar' );
function portfolio_sidebar($sidebar){
if(x_is_portfolio_item()){
return 'ups-sidebar-portfolio';
}
if (get_post_type(get_the_ID()) == 'mec-events') {
return 'ups-sidebar-portfolio';
}
return $sidebar;
}
Change ups-sidebar-portfolio
with the ID of the sidebar which you created:

Change mec-events
with the slug of your custom post type.
After that, you can go to Appearance > Widgets and assign widgets to the sidebar you created for the custom post type.
Thank you.