Can You try "uploaded files" in the Adminconsole - this loads the files to /data/_uploaded.
* If You load pictures with ckeditor, just click at the site -> ckeditor -> image symbol - > browse server etc.
The above picture looks otherwise like like a bad installation. Evtl. You can remove the error with "tools/uninstall prep -> restore" which resets the rights.
I prefer ftp - installation with filezilla portable. Other users had problems with other ftp-clients before ! (it may already help to overwrite the /include - directory with filezilla)
After transfer just klick at the installation-directory and right mousekey : 755 - also for subordinate directories and files - and then install from the browser.
The problem is unclear. Have You saved (and published) the site before You tried to upload the picture ? It looks like an error in the code of the site. Can You try to upload a picture in an empty new site ?
Do You have the same error if You go to "content > upload files " ? Do You use a WebControl panel like Plesk ?
( Evtl. You should better the CMS install into a subdirectory of the root because of filters of the provider. Can You try another installation with with filezilla --- and use the CE-Version or the github master (most advanced) instead of the 5.1 which is not really php7.3+-ready. )