I am not sure this is a bug in this module, or a bug in core, but when a file contains a character such as % the link to the file returns the an unecoded url which results in a 400 error from S3 when linking to it.
When using Drupal's standard public or private streams the urls are encoded correctly.
I have only tested using:
Use a file with a % in the filename - e.g this is 100% not working.pdf
Evaluating this code - (taken from what is happening in template_preprocess_file_link)
$file_url_generator = \Drupal::service('file_url_generator');
$url = $file_url_generator->generate($file->getFileUri());
$url->toString();
When using Drupal's public file system the URL is returned as: /sites/default/files/this%20is%20100%25%20not%20working.pdf
When using the S3 public system take over the following URL is returned: https://buckerurlexample/public/this is 100% not working.pdf?VersionId=....
With the lack of encoding in the link - I get a 400 response from S3 - visiting https://buckerurlexample/public/this%20is%20100%25%20not%20working.pdf?VersionId=.... returns the file as expected.
Debugging it looks like the URI gets encoded in the UnroutedUrlAssembler::buildLocalUrl method for the standard public / private files - https://git.drupalcode.org/project/drupal/-/blob/10.2.6/core/lib/Drupal/...
However when it is an external URL is no encoding on the URI passed in buildExternalUrl
TBC
TBC
n/a
TBC
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Active
3.0
Code
I believe this is going to be a duplicate of #3314663: File links for paths with reserved characters ( '+' & '#' '?') generated wrong for external streamWrappers. →
Not noted in the other issue however IIRC the difference in core vs s3fs is that internal routes take a different code execution path with different manipulation.