Accessibility violations

+1 for this issue.

Is this an issue on the 4.0.x branch as well with jjj/chosen?

I'm maintaining a copy with a11y fixes at https://github.com/ckng/chosen. You can download the released zip.

Instruction for Drupal: https://github.com/ckng/chosen?tab=readme-ov-file#to-replace-drupal-chos...
Reproduced here:

Extract the released zip into THEMES/js/chosen, for example, where THEME is your theme name.

In your THEME.libraries.yml:

chosen:
  remote: https://github.com/ckng/chosen
  version: 2.2.1
  license:
    name: MIT
    url: https://github.com/ckng/chosen/blob/master/LICENSE.md
    gpl-compatible: true
  js:
    js/chosen/chosen.jquery.min.js: { minified: true }
  dependencies:
    - core/jquery

chosen.css:
  version: 2.2.1
  css:
    component:
      js/chosen/chosen.css: {}

In your THEME.info.yml, override fully the default from chosen_lib.

libraries-override:
chosen_lib/chosen: THEME/chosen
chosen_lib/chosen.css: THEME/chosen.css

Let me know if 5.0.0 still has accessibility issues.
It has a new fork with some improvements.

After installing 5.0.1 and running an accessibility check (using axe DevTools Chrome extension) on a page that uses Chosen, the following error is flagged with the following solve:

Elements must only use permitted ARIA attributes. Ensure ARIA attributes are not prohibited for an element's role
Element Location: #edit_affiliation_chosen > .chosen-single > div[aria-label="Show options"]
<div aria-label="Show options"><b aria-hidden="true"></b></div>
To solve this problem, you need to fix the following: aria-label attribute cannot be used on a div with no valid role attribute.

A possible solution could be to change the code to <div aria-label="Show options" role="listbox"> with a role added. Doing this and running the scan again eliminates the error.