Yeah, one of the devs finally messaged me with this solution where you basically have to give it the correct permissions. The tricks in the download page is needed as well but not enough. Here is what he wrote me:
"I got it working on the mac (m1 air) using these commands in terminal:
cd /Users/MYUSERNAME/Downloads/Stacklands_v1.0.5\ \(macOS\)
(you can replace the thing after cd with wherever the .app is located in your filesystem... the easiest way is to type 'cd' and then drag the containing folder itself into terminal, it'll copy the path right in)
chmod a+x Stacklands.app/Contents/MacOS/Stacklands
xattr -cr Stacklands.app"
Hope this helps you as well :)