@Chaki-09 As pointed out, Brave does have native PiP mode. Some websites like Netflix may code the website to try to prevent this for a variety of reasons and Brave tends to honor that when it’s in the web code to prevent picture-in-picture.
There has been a lot of prior talk on this in the past if you would care to search through existing topics, such as Picture in Picture (PIP) Not Working on Xfinity Stream