Does this work?

https://playingcards.io/docs/custom-decks

Haha, how did I miss that? :D

Yes this looks nice! Though I was also thinking of a way to just upload images that can then be used.

This will be perfect for a lunch and learn series on probability fundamentals I want to hold.

Tabletop Simulator has pretty much every card and board game you can think of as a fanmade mod. There's also a scripting system and official virtual versions of commerical games that use the scripts to automate parts of the game like setup.

Shameless plug - but give https://screentop.gg a try! Studios and kickstarters are already using it to develop and play deck building games.