Are your files transfer options greyed out in your Android phone, like on the picture below?
Do not panic. And do not waste your time like I did trying to sort out why it happened. Just… change the cable. Suprisingly the “bad” cable I was using was relatively short cable which was absolutely fine for othe different USB devices – I was able to transfer data without any problems. But the cable just did ot work for my Pixel phone. After replacing the cable with a different one, there was no problem at all:
