I'm more of a risky gambler, but I would bet it lasts the full 5 seasons. I don't know the intricacies of the business, but it sounds different from other projects in the business.
The difference with Rings of Power being they already purchased rights to film a 50-hour show. So there's already a definitive end and the creators have claimed they have the series planned out to its full conclusion. And based on how little is progressing in Season 1, there doesn't seem to be any urgency to conclude anything. It suggests assurances that it will conclude with 50-hours of show time.
https://movieweb.com/the-rings-of-po...0-hour%20show.
I don't know if it's possible for them to purchase more than the 50 hours? That is, even if it was super successful, it doesn't sound like it could go beyond the 5 seasons. But I would feel safe betting there will be the full 50 hours.