Applying a transparent background to react native is simple. below is a code just similar to the normal css for html pages, but just that it contains the react native styling type.

backgroundColor: 'rgba(52, 52, 52, 0.8)'

a good example is below

 <Box
             flex={1}
              backgroundColor="lightblack"
              justifyContent="center"
              alignItems="center"
              style={{
                backgroundColor: "rgba(52, 52, 52, 0.2)",
              }}
            >
              <Spinner color="white" />
            </Box>