My way of getting around it was manually installing the Forge version that Twitch is trying to find. Just get the exact version of the Forge Installer from their website (in this case 1.15.2-31.2.30) and set the install directory to "(Your-twitch-client-directory)/Minecraft/install."
1.8685447169546
I've had this issue with Modpacks beyond 1.12.
My way of getting around it was manually installing the Forge version that Twitch is trying to find. Just get the exact version of the Forge Installer from their website (in this case 1.15.2-31.2.30) and set the install directory to "(Your-twitch-client-directory)/Minecraft/install."