Hmmm - if this is what you mean, you'll see that I get plugin .zips and .jpgs in Sigil jump lists :
I never use Sigil's jump list so I've not noticed, I either use Sigil from Windows or Calibre's built-in Open With.
But, I see that Sigil is in Windows Open With list for both .zip and .jpg - pretty sure I didn't put them there.
BR
I changed the taskbar icon so I could see it