You can choose different effects for inbox zero (from nothing, to Gmail's illustration, to various backgrounds) in Simplify's settings. If your trial has expired and you'd like to extend it to try this, email me at hi@simpl.fyi.

Gmail's dark theme is NOT hidden behind a subscription. Simplify works for two weeks for free during the trial period and then it requires a paid plan ($2/month) as the extension requires on going work to keep it working (see this post for details: https://on.simpl.fyi/p/complexity-of-simplify).

But I do NOT hide any Gmail features during the trial or after.

UPDATE: Thanks for the added star. And understood about the paid plan. Please note that ALL of Simplify's functionality requires a paid plan after the free trial period is over. This is stated on the extension page and in the extension itself upon installation. So, I'm not sure what is shady here. Your statement that "Also hiding dark theme behind the subscription is super slim shady" makes it sound like I am hiding Gmail's dark theme.