Link exchanges is not that good.
However you can go for guest posts. There are many sellers here or you can even outreach and get some links.
If your content is good, the blog owners might give for free. Else they normally take some charge
PBNs have always worked. But make sure you do due research before purchasing links from any sellers. I have used pbns many times and they work and help in increasing the rankings. So yes even if its 2020, they are working. Just because a year has passed, doesnt mean a method becomes obsolete.