I propose to make the “Minecraft” theme free for all registered users. Due to the large audience of this game, more people will be interested in your app and they will want to use other themes for games that will come with a subscription. This way they will be forced to purchase the pro version.
The fact is that the most interesting functions are found in game integrations. Due to synchronization with the game, users will register, and as soon as they understand that all game integrations are paid, they simply become not interested in buying a subscription (also for a limited period) and they delete your application and thereby you lose your users and money.
It’s the Minecraft integration that will give you the sales promotion you need + most YouTubers will help you with advertising and attracting new users.