I used Google App Engine around 10 years ago for my pet project and it worked just fine, for free. I didn't use App Engine since then. This year I have got an another idea I wanted to implement and wanted to use App Engine again. A lot has changed, and I had to add my payment card now, but I managed to deploy the app to us-west1 region and get it working, for free. However, at the end of the month I was surprisingly charged for a couple of dollars. Investigation of the billing report showed, that I was charged for Cloud Storage - the service that my app doesn't use at all! Further research showed, that during the deployment a multi-regional Cloud Storage "...artifacts...appspot.com" bucket is created in the background and something gets uploaded there on behalf of my app. Multi-regional buckets aren't free and I need to pay for any data stored there! I may delete the data from that multi-regional bucket after the deployment, but something gets uploaded there again on every deployment. I cannot prevent that.
So, running an App Engine app with low load is indeed free, but deploying any changes is not free, every time. Is it an expected way of implementing modern free App Engine? I want to believe that it's me doing something wrong and not Google playing marketing games with me by calling App Engine free and staying silent about the inevitable deployment costs. Can you guys shed some light on this situation?
No, you aren't doing anything wrong. That's the behavior of GAE now.
Code deploy leads to the creation of a multi-region bucket for which you're charged a few cents. If you're charged a couple of dollars, it's probably something else.
Previously, you could delete that multi-region bucket after deploy but that now gives an error (see this stackoverflow question)