I already repaired .NET and C++ runtimes to fix the Synapse problem, which has been solved. The mouse issue is related to when my second monitor (smart TV) is off, and for some reason Windows 10 sometimes doesn't except the termination signal and tries to connect to the monitor every 7 seconds exactly, causing the mouse to hiccup for whatever reason.
I also don't have any problems with any other software relying on C++ like Blender, ZBrush, Unreal Engine, or games like GTA.
The problem started with TG not detecting the runtimes already installed, trying to directly install over, creating a Installation Blocked error, and TG exiting. I then uninstalled the runtimes and let TG install them, which also for some reason reinstalled Visual Studio according to windows prompts with the Runtimes.
Uninstalling and Reinstalling Terragen doesn't have any issues detecting runtimes, and installs right away.