It's a BL project :) if you read the book you may understand the BL parts from the series way better, the most direct ones are, the fact that they end up cultivating together ("combined" cultivation) it's explained in the book what it means, in the series, the meaning is only hinted by Jiang Cheng's mother and the second one is our main guys "wedding" scene. There are a lot of scenes that have hidden meaning, they are not explained with words but are shown, it's up to the people to research the meaning, if not there are a lot of Chinese people that have explanations on youtube for the scenes (if people didn't read the book), explaining, names, traditional things and meaning, legends and inspirations and other hidden messages or symbols that are connected and deeply embedded in Chinese traditions and culture. Also, the soundtrack is also very important as each song is representing the main characters and the lyrics are important as well, they were specially chosen for a reason. The international special edition version is made even more obvious.
The story at first was written first with Wei Wuxian and Wen Qing as "main-couple", the information was leaked during filming and the fans boycotted the series so they made an official declaration saying they will keep it as the book. In the end, even the official description is "adaptation was censored with homoerotic subtexts instead due to China's ban of LGBT portrayals in films." Even the director talked about certain scenes and explaining the meaning.
Even if it's not an open BL it can 100% be a Bl 'hinted at' project, but for the people that understood the easter eggs, it's obvious.