Is PBN still good for building backlinks?

yes, the quality of the domain and the way links are placed matters far more than the fact that it’s a PBN. When done carefully and mixed with other natural signals, it can still give a noticeable push

PBNs work as long as links work.

But it's crucial to understand the difference between links that you can buy from public networks and PBN that you own.

"PBN" links that you can buy most often don't bring any value, while links from your own PBN work just fine.