Basically, the CurseForge App cannot install the required Forge version, which is why we get the error "The system cannot find the file specified".
To resolve the issue manually, I had to find the forge version required for the modpack I wanted, As of 12/16/2020, ATM6 is using Forge Version 35.1.13. After manually installing Forge version 35.1.13, I was able to download the modpack via the CurseForge App and launch/play.
Once you find the Forge version you need for the modpack, download the Installer from the official Forge site. Once downloaded, install the Client into the 'Install' folder of CurseForge instances (Mine was C:\Users\[YOUR COMPUTER NAME HERE]\Twitch\Minecraft\Install).
You can also find this by opening the three dots of a previously installed modpack, clicking 'Open Folder', then clicking 'Minecraft' in the directory up top, and opening the 'Install' folder. Click the white space next to the text in the directory and CTRL+C the text with the slashes, open the Forge Version you need, and CTRL+V and open.
Once installed, simply click 'install' on the modpack you want. For ATM6, I recommend at least 8 gigs allocated in order to run smoothly.
Hope this helps, I'll try to check for replies to help later on <3