The fact it doesn't exist doesn't mean it
can't exist. The only reason ads are so prevalent is because they're the easiest and most lucrative way to monetize, at the expense of the user.
FWIW I think the Brave Browser model is a step in the right direction, even though Brave Inc. has made some missteps along the way. Give the user the choice of which services they want to support, and make that process as frictionless as possible.
If the tech giants had incentives to come up with a user-friendly business model, I'm sure those genius minds would think of something. Alas, the status quo benefits their shareholders and they have no reason to change.
FLoC is just marketing fluff to paint their predatory practices in a better light, not an indication that they actually care about their users. Their #1 priority is still profit from advertisers.