I have this exact same use case for an app I’m building and would love an answer as well. I built on S3 as a result. When a product says “full S3 api compatibility” this becomes my question.

Going further I don’t want to become someone else’s back door file repo for illegal shit. So presigned upload urls with an enforced file name and configurability over the size limit and expiration of the presignedpost (both in terms of time and number of files) is pretty important to me. S3 does a good job here.