I try to launch Galaxy and get this error.

WIndows can't find GalaxyClient. Yet, I'm launching that file from the GOG Galaxy folder.

I've tried uninstalling, reinstalling, updating, compatibility mode. Nada

Install both vc_redist.x86.exe and vc_redist.x64.exe then restart your system.

If that doesn't help, double-check your Windows environment variables:
1. Press the Windows logo key + Pause/Break on your keyboard. This opens up Control Panel - System and Security - System.
2. Click Advanced System Settings on the left. This opens the System Properties window.
3. On the Advanced tab, click the Environment Variables button in the lower right corner. The values of Path and PathExt can cause problems when modified incorrectly. Post a screenshot of them here if you're not sure if that's the case.

Your issue aside, note that you might not actually want the latest version of GOG Galaxy at the moment. It has a background service that crashes constantly. Some of us have downgraded to 2.0.75.142.