The DSD+ console does say "No supported tuner found"
Can you tune to any known frequency and receive it with FMP24?
The 'FC0012' tuner should be supported via the RTLSDR driver.
Possibly the problem with gain in DSD+ is that the 'FC0012' does not seem able to report any supported gain values which DSD+ maybe expecting.
You may need to manually set the gain option (-g<num>) in your startup batch file to be able to change it.
According to the (RTLSDR) source code of the 'FC0012' tuner, the default gain is 192 (19.2dB) and the other supported gain values are -99, -40, 71, 179.
Contacting DSDPlus may be the better approach as they can inform you if it's supported or could be in future versions.