The way you build the PBN is super important. Firstly if you get expired domains (something I never recommend doing) make sure to check every single bit of their history, they might hold shitty links within that are not that easy to track.
Then, start treating them as a normal domain, write loads of content, make sure to maintain the freshness on a monthly basis and overall just work on it as if it was your website. After a while (depending on amount of articles/images/etc) you are good to start linking.
The main problem is that people build a pbn n start linking straight up, not only that but they also end up with tons of OBL... and that just devalues it and makes it PBN obvious.