Hi,
In Magento 2.3, While uploading a logo via Content->Configuration->Design->Edit->Header->Logo getting a error like "header_logo_src does not contain field 'file'" but already I have changed the file /vendor/magento/module-theme/view/adminhtml/ui_component/design_config_form.xml
and changed "fileUploader" to "imageUploader". But still getting the error.
Here is a screenshot, kindly do needful.
check with the correct theme file or else by overriding the xml file.
https://github.com/arshadpkm/magento-2.3-header-logo-upload-bug-fix
i Had the same issue and could rectify using
for Favicon and Logo :
https://github.com/magento/magento2/commit/ba69bfec127bed8c39c7d9e7b73d10b54449b158
for transaction emails :
than i ran following commands on developer mode.
$ php <magento dir> bin/magento indexer:reindex
$ php <magento dir> bin/magento cache:clean
$ php <magento dir> bin/magento cache:flush
and things worked again