What .deb file? Their page says to add a repo and use apt:
sudo apt install curl
sudo curl -fsSLo /usr/share/keyrings/brave-browser-archive-keyring.gpg https://brave-browser-apt-release.s3.brave.com/brave-browser-archive-keyring.gpg
echo "deb [signed-by=/usr/share/keyrings/brave-browser-archive-keyring.gpg] https://brave-browser-apt-release.s3.brave.com/ stable main"|sudo tee /etc/apt/sources.list.d/brave-browser-release.list
sudo apt update
sudo apt install brave-browser
My brother in Christ, installing a .deb is downloading the .deb directly, as you would when downloading discord from discord.com, and you use dpkg to install it (apt uses dpkg to install the deb file).
You saying “the deb file” is not the same as “using the official repo”, as dependencies might not have been installed by only using the .deb file.
Make sense?