[haxxorfreak]

Aperture is actually a 64-bit app but it depends on some system frameworks that weren't migrated to 64-bit and dropped in Catalina.

It's possible to get it running in 10.15 by removing the references to those frameworks, it breaks some of the features like slideshows but the app will still run: https://medium.com/@cormiertyshawn895/deep-dive-how-does-ret... (the author has also made an app that automates this process, I haven't tried it so I can't vouch for how well it works)