I did a careful read through of the original journal article and I have a few observations.
First, the study is a well-designed prospective study conducted at 75 sites across Europe. That is, the study authors selected participants ahead of time and then followed them over the ensuing years. Second, the study period lasted for about 7 years, with the median couple being followed for 2 years. This means that the study was able to look at roughly 1,600 couple-years’ worth of data, representing over 76,000 instances of unprotected sex. In that time, there were 0 instances of within-couple transmissions of HIV.
Taken as a whole, this study strongly suggests that the risk of HIV transmission in condomless sex when HIV viral load is suppressed is effectively zero.
[https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(19)30418-0/fulltext](https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(19)30418-0/fulltext)