Before I started I had to make sure my mac running on Big Sur can accept software installs from Anywhere. In Big Sur Apple removed that option for the users but you can activate it by running this in your terminal sudo spctl --master-disable Then, I tried with the posted instructions here for homebrew, but actually, something went wrong so I went to their official website at brew.sh and got their installation code from there. Its this one /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" After you type this in the terminal, you wait for the install and then you type: brew install upx For me, it didn't work putting the file on the desktop, so I put it in Applications, and then I wrote this in terminal: sudo upx -d (and here instead of writing the directory its best to go to Applications Right click xf-adesk19 and choose Show Package Contents Contents MacOS x-force and simply drag and drop that file after the -d in your terminal and it should visualize the path) And then press enter, and now u should be able to open that file on MacOS Big Sur. Note if you already tried using the install code from this post and it didn't work, first run a Homebrew uninstall with this code: /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/uninstall.sh)" And then run a fresh install with the code I just wrote. Hope this helps.