the STM32H753bi.pdf datasheet Rev1 tells on page 2:
3× ADCs with 16-bit max. resolution (14 bits2.7 MSPS, 16 bits 168 kSPS)
This would imply a 14-bit SAR adc and 16 bit as a result of oversampling.
In chapter 6.3.20 16-bit ADC characteristics on page 157 of the dataheet however a sampling rate of 3.6 MSPS for 16-bit is given. This implies a 16-bit SAR block.