Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/Microchip Technology/ATSAME51J19A/DAC/CTRLB#0x0
REFSEL=VREFPU
Control B
Differential mode enable
Reference Selection for DAC0/1
0 (VREFPU): External reference unbuffered
1 (VDDANA): Analog supply
2 (VREFPB): External reference buffered
3 (INTREF): Internal bandgap reference
https://github.com/cmsis-svd/cmsis-svd-data