To install gocryptfs, macFUSE is required, which relies on a license not accepted by Homebrew.
This is why the upgrade command refuses to work.
Installing or updating via homebrew fails for this reason.
Here you learn how to manually install and update gocryptfs.
As precondition, ensure you have Xcode, git and the "Go" programming language installed:
xcode-select --install
brew install go
brew install git
Remove any old version of gocryptfs via brew uninstall gocryptfs.
Update or install macFUSE, either by downloading it from macfuse.io or using the homebrew command:
brew install macfuse
You need to allow the macFUSE system extension within the "Security & Privacy" system setting and restart your Mac.
Then, download the gocryptfs source code and compile:
git clone https://github.com/rfjakob/gocryptfs.git
cd gocryptfs
./build-without-openssl.bash
The command compiles and installs gocryptfs into the directory ~/go/bin.
To be able to access gocryptfs directly in the terminal, add the folder in which the tool is installed to the search path.
This can be achieved with echo -n 'export PATH=$PATH:$HOME/go/bin' >> ~/.zshrc.
In case you mount your encrypted directories automatically with an Automator workflow or a LaunchAgent, you need to change the absolute path /usr/local/bin/gocryptfs to /Users/<NAME>/go/bin/gocryptfs.
Replace <NAME> with the folder name of your account. You can also find out the correct path by typing which goctyptfs.