2
This is a symptom of SDA being pulled to ground.
Test your GPIO with nothing connected to the extension header.
See https://elinux.org/R-Pi_Troubleshooting#Testing
1
The reason your I2C sensor isn't detected is that you've not soldered the header pins into the breakout board. There won't be a connection between Vin, GND, SDA & SCL to your RPi.
The BME280 on your breakout board runs on 3.6V max, so don't connect Vin to either pin#2 or pin#4 use pin#1 or pin#17.
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