Hi,

You can filter your slider by use a "Tag".

As I see you're using Elementor to config your homepage, so you can do follow steps below:

1/ Go to Dashboard > Posts > Tags > create a new tag - example:   "featured"

2/ Add more this tag to all the posts you want to show on the slider

3/ Go to edit your homepage by use Elementor > right click on the slider you want to filter by the tag "featured" and select edit this slider > on "Query" section on the "Tags" select "featured" tag you've created before - check this image: http://prntscr.com/vvft19

Best Regards,

PenciDesign