To resolve the conflict, you will have to remove the Garuda Network Assistant package. Whether or not that is a worthwhile sacrifice is something you will have to decide for yourself.
The alternative is to remove the conflicting packages with pacman -Rdd to skip dependency checks. This method is not recommended because messing around with dependencies is risky from a package management perspective (and can lead to headache and anguish), but perhaps you may wish to consider it anyway.
A third option would be to not install all the tools, just install the ones you need. To list all of the available tools:
pacman -Sgg | grep blackarch | cut -d' ' -f2 | sort -u
To see the tool categories:
pacman -Sg | grep blackarch
To install a category of tools:
pacman -S blackarch -<category >