Homebrew Casks are used to install pre-compiled applications. A lot of those come with their own update mechanism, so having them update both internally and via brew upgrade leads to issues. There is a section in the Homebrew FAQ covering this.
From that section:
Anything installed with Homebrew Cask should behave the same as if it were installed manually. But since we also want to support software that doesn’t self-upgrade, we add
auto_updates trueto casks for software that does, which excludes them from brew upgrade.
The formulae for both Discord and Figma have auto_updates true set.
This means that any update will be triggered by the application itself. These update mechanisms aren’t aware of the changed folder location though (this only impacts Homebrew), so they either get confused or install the update to the default place.
The easiest way out of this probably is to install these applications to /Applications (and not onto an external disk). If you are low on disk space, you can also disable auto-update within the applications (or cancel any update attempt) and run brew update discord figma regularly (which will force a Homebrew-driven update even for self-updating applications).
PS: As far as I can see, at least Discord doesn’t allow to prevent auto-updates. Running brew update discord before starting it may the best option then.
