I didn't tested on fresh mac, so i can only theorize, solution must be simple, try this, immediately after trying to open RocksmithTool:
System Preferences => Security & Privacy => Tab "General" => Allow anyway
Hi everyone, just started to use Rocksmith and faced need to convert packs to mac format but found out every existing easy solution for mac is outdated.
So i figured out how to run rs-toolkit on wine and considering lack of convenient ways to run it on mac, I decided to resolve it myself
https://github.com/helioxigen/rocksmith-toolkit-mac
Here you can download installer for Rocksmith Toolkit wrapped in wineskin with 32on64 support
Tested on latest Big Sur (11.4), so any macOS 10.15+ should be supported as well