I found the root cause, here is the solution if someone face the same issue. The fact that the project was using Capacitor HTTP, was working under Capacitor 5 for AWS Client (@aws-sdk/client-s3) but no more under Capacitor 6 and 7 (tested both).

in file capacitor.config.ts :

 "CapacitorHttp": {
      "enabled": true

This was a requirement for some other webserices that I should call. So what I did, is to set them off :

in file capacitor.config.ts :

 "CapacitorHttp": {
      "enabled": false

This made working @aws-sdk/client-s3 under Capacitor 7 but was problematic for my other Webservice. So I recoded manually and explicitly my other using import { CapacitorHttp } from '@capacitor/core'; and removing all references to Angular HTTP.

I'm always very impressed by people who spend more time downvoting a ticket than providing a solution. So if you have issue on your @aws-sdk/client-s3 transmission when updating Capacitor check the CapacitorHttp, there's breaking change in the comportement between v5 and v6+.