Other way to handle downloads that I find convenient is to have the Brave-portable64 directory in /mnt/home , and in the settings change the downloads directory to /mnt/home/Brave-portable64/PROFILE/spot
Since /mnt/home/Brave-portable64/PROFILE/spot is already owned by spot there is no permissions problem and the downloaded files are "portable" too (i.e. inside the /mnt/home/Brave-portable64/PROFILE/spot dir, rather than inside the system (/home/spot/Downloads).
But it depends on what's preferred of course.