Hello, Deepl. will be my interpreter for the rest ;-) I've been struggling for a few days now, but I've just found a solution that worked in my case. I've been going round and round in circles, and I've come to believe that the problem is not about Big Sur giving permission to the application, but more likely a problem between UPX (since we're talking about an application compressed with upx) and Big Sur. That said, it is possible to see that the compression with UPX must be kept, otherwise the application (its Unix executable in fact) that has been decompressed will instantly disappear from the screen... To get around all these constraints I did some manipulations in a less aggressive environment, namely a Mojave virtual machine that I had to create for the occasion (Catalina would perhaps also be suitable...). Under Mojave then : 1) Uncompress the app as said above : upx -d [/...]/myApp/Contents/MacOS/myApp 2) Re-compress the app, but at the minimum level to preserve compatibility with Big Sur : upx -1 [/...]/myApp/Contents/MacOS/myApp That's all ! The app is now supported by Big Sur and can be launched directly :-) Hopefully this will help a lot PS : At the end of the process of using the app, I got an error message (from the target app) which had no consequence on the intended purpose.

Homebrew is well installed on your MB?