Apollo did have a free tier and then a few paid tiers.
iirc, (I bought it many years ago), they had a one time Pro purchase that removed any ads and unlocked theming and such, and then the Ultimate which was a subscription to cover server costs of push notifications (although it did eventually end up having more features locked behind it).
While I personally did not go for the Ultimate subscription (didn’t really need the push notifications), I gladly paid for the Pro as it was well worth it IMO.