There's a difference between delisting your app from the Shopify App Store and making it private (now called custom). A delisted app still needs to use Shopify's billing system and pay the 20% fee even if you find new customers yourself. If your Shopify app is private (custom) then it doesn't need to use Shopify's billing system but then it can't be installed by more than 1 merchant. So Shopify has basically created a catch 22. If you want your app to be installed by more than 1 merchant even if it's not on the Shopify App Store then you're required to pay them a fee. For reference, Shopify made this change at the end of 2019: https://www.shopify.com/partners/blog/shopify-public-apps