Failed to launch child process

Don't know your IDE.

But general experience tells me that many applications cannot deal with several instances at the same time, and refuse to start under that circumstances.

I would check if some comatose instance of gdb.exe is still running.

And, of course, that the executable is still there.

For some reason all of a sudden it worked for some weeks and now I get the same error again out of the blue. Reboot of the PC with ST visual only did not solve the issue.

I had the same issue. uninstall and reinstall method did not work.

Update your windows, it works.

A few days ago, I made a mistake and left the weight on the return key, and a lot of STM32CubeIDE started up. I forcibly rebooted the PC in the middle, but after that I couldn't access ST-Link at all, so I had no choice but to process it on another PC.
Today, when I tried to debug with STVD (for STM8), I got the same message as the questioner. I thought that the ST-Link driver might be broken, so I reinstalled it, and it returned as if nothing had happened. Is it possible that the driver is corrupted?