I'd like to use conditional fields in my CMS instance. I found an old plugin called Reasons. I'm not sure it's compatible with Craft 3, so I'm looking for a workaround.
I really miss the Reasons plugin and am disappointed the makers of Craft didn't roll it in to Craft 3.
Not quite what you're looking for, but you could try using the Control Panel CSS and Control Panel JS to add lightswitches that show/hide specific fields. You could start with the field hidden, and require a click on the lightswitch to show it.
It's a bit of a hack, but can work well.