💬 In the SPLOT Footnotes it says 1. you can add your own features
It’s a matter of installing and activating the Easy Footnotes plugin.
Using it when writing, is a matter of starting at the point you want the footnote attached, adding an [efn_note] shortcode then the text that you want to appear in the footnote, and closing it with the ending [/efn_note] shortcode.
Still living the dream that is the text editor, I use Post Editor Buttons Fork to help add in snippets of code.