So there's no way to add a spell DC to the "Hit/DC" field when it's added from an Action? Only when it's a Spell?

Action. and below is the information for it:

but as you see below, it does correctly show up if you create a whole spell for it. which seems utterly ridiculous:

Adding insult to injury, you can add a spell save dc, but only if it's fixed:

painted the number because I didn't want to get another screenshot. but u get the idea:

Answering my own question
It works as long as you don't select melee/ranged in the attack range field at the top