Bit depth is different from internal processing precision. Your MOTU 828 MkII can capture audio with a bit depth of 24 which can already be processed with 64-bit float precision in Cubase (since 9.5) as long as you only use VST3 plugins that are capable of processing with 64-bit float precision. Further information here.
What’s new about the UR816C compared to the MOTU 828 MkII is that the analog-to-digital converters (ADC) are capable of digitizing the audio into 32-bit samples vs. 24-bit samples in the 828 MkII. A bit depth of 24, as in the 828 MkII, already gives you a theoretical dynamic range of 144dB. For comparison, the difference between a quiet room and a jumbo jet taking off over your head is about 90-100dB. Will you need a dynamic range of more that 144dB?
An analog-to-digital converter with a resolution (bit depth) of 32 bits has a theoretical* dynamic range of 192dB, but that’s around the threshold where sound, in air, ceases to be sound and becomes a shock wave. No musical instrument can create such dynamics, and no microphone can record it.
*it’s going to be much less in reality because of the limits (noise) of the analog electronics surrounding the ADC