Reddit gets paid either through ad revenue displayed to non-paying visitors to the website, or through API calls for access to their dataset. Apps that enable user access via the API will need to pass along this charge to their users.
Apollo must become a paid-subscriptions-only app, as Reddit now charges for usage. This is fine. Apollo needs to constantly be updated to keep up with Reddit API changes over time anyways, so neither 'free' nor 'one-time purchase' are acceptable ways to provide a continuous living wage for keeping up with reddit API (and mobile OS) updates.
There's a third (paid) option, which is that Apollo sells the app to Brave or Firefox, where it's integrated into a paid "Reader Mode" subscription — because a team of developers will need recurring revenue for living wages in order to maintain the website rendering overlay and overcome Reddit's attempts to block or break it, and will need a team of lawyers to defend against the eventual lawsuit Reddit will bring against them (even if they'll lose due to the LinkedIn precedent from a few months ago — but, I am not their lawyer, this is not legal advice).
There are no good free outcomes that are not advertising-supported, and the API is incompatible with advertising, which is why so many people use it. I'm glad to see that Reddit has realized this, and I'm glad they are still offering the free ad-supported website rather than a paywall. I hope that Apollo is willing to charge me for their app, and isn't demoralized by their users complaining about this. We'll see.