Hi Gunasekar,
Is DMAMUX necessary?
>> No, if you want to use a trigger to change the resource input for DMA channel, then you use DMAMUX for switching. ADC can be configured with DMA transfer, which not necessary to configure DMAMUX if you don't want to change DMA resource during runtime.
1>> Please share your project. or share the configuration files, the version of driver that you're using too.
I need to check your configuration directly.
2>> DMA already had clock source for it, as hardware design. So as far as Mcu configuration already have the clock sources, the clock source will be applied to the DMA, so it's not be configured in any components.

Please share your project/configuration and driver version.
Thank you,
Nam.