Didn't test with upload widget but with 'View' widget we cannot select SVG images because the image extensions are hardcoded in the validate function of the 'View' 'FieldWidget'.
Usecase: Install https://www.drupal.org/project/svg_image → so image fields can support SVG images. Go through your image fields and update the extensions to include SVG. Then try creating a node or an Image entity with SVG. Using the default image widget works fine. But using the EntityBrowser View widget throws an error on selecting the SVG because of the hardcoded extensions in the validate function.
Should we let the the extensions settings of the field dictate what type of images could be added using EntityBrowser and EntityBrowser was not opinionated?
Needs review
1.4
Widget plugins
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
This patch stopped working in 2.10 and is still an issue. I've opened an MR.
https://git.drupalcode.org/project/entity_browser/-/merge_requests/44