From the BME280 datatsheet:
The 7-bit i2c device address is 111011x. The 6 MSB bits are fixed. The last bit is changeable by SDO
value and can be changed during operation.
Connecting SDO to GND results in slave address 1110110 (0x76); connection it to VDDIO results in slave address 1110111 (0x77), which is the same as BMP280’s I²C address.
So the address can be both.