I performed a clean install of Jenkins 2.33 (and 2.37) into Windows and although the S3 plugin installed, the sub-section of "Configure System" for "Amazon S3 Profiles" did not appear. There were no errors in the logs; all plugins loaded successfully.
In order to get the credential section to appear, I had to rip out version 2.x and install 1.609. Once that was done I was able to configure my S3 profile. Updating to 2.x after the fact did not break this - it is still working properly.
It seems as though there's a requirement buried somewhere in 1.609 that gets carried forward after an upgrade but that isn't present in a clean install of 2.x. Either the plugin needs to be updated to work correctly in a clean build, or whatever holdover is present needs to be brought forward to the 2.x series.