Using XXX Expired Domain Sites

Not an issue here - any domains are fine for a PBN - as long as they've not been spammed before and have a good quality link profile. Obviously it's better if all sites are in your niche so they look more relevant to your site though.

I would avoid anything with Spammy backlinks I would also avoid anything XXX related

Try to buy expired domains on your niche related.

If the site has adult backlinks you should not use it in your PBN it will most likely negatively affect your site.

Like others have said if it has adult backlinks I would totally avoid it... I wouldn't want adult content linking back to my money site.

I don't know about you thread starter but you should know that adult sites or triple X sites have historically been viewed by search engines as "bad neighborhoods".

If you're going to build a backlink network using the expired domains of these types of websites, you are drawing unnecessarily bad attention to yourself.

I hope this much is clear.

So if I were you I will steer clear of the temptation of using expired triple X domains that may have quite a bit of backlinks.

At the end of the day, those backlinks and that link equity doesn't help you all that much if you're pointing all these expired domains to a website that is not pornographic in nature.