I never used Fiona with AWS, but I suppose this is mainly dependent if GDAL supports it. GDALs issue tracker seems to contain a relevant entry:  https://github.com/OSGeo/gdal/issues/2470
This issue was fixed with GDAL 3.2.0: https://github.com/OSGeo/gdal/blob/v3.2.0/gdal/NEWS

How to set credentials in Fiona is described here:  https://fiona.readthedocs.io/en/latest/manual.html#cloud-storage-credentials