There will be two versions of libstdc++... in Gimp one 32 bit and the other 64 bit. I was thinking more about a conflict in the main Windows system. However that is not the problem. You gave the solution, Gimp 2.10.14 The latest gmic_gimp_qt (2.9.7) was 'fixed' for Gimp 2.10.24 (see that bug report) and that breaks it for Gimp 2.10.14. I can get that error message.
Use the previous version of gimp_gmic_qt https://gmic.eu/files/windows/gmic_2.9.6..._win64.exe
Delete the whole gmic_gimp_qt folder in C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\plug-ins and install the 2.9.6 version.
Use the previous version of gimp_gmic_qt https://gmic.eu/files/windows/gmic_2.9.6..._win64.exe
Delete the whole gmic_gimp_qt folder in C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\plug-ins and install the 2.9.6 version.