Edit // I upgraded my moodle version to 3.10.3+, I don't get ajax error anymore, my copy problem is solved,
However, I could not recover my old file unfortunately 
I saw an error on the Google Chrome console, when I did the copying process, it pops up an error about jquery as in the appendix.
jquery-3.5.1.min.js:2 POST https://halimasa.com.tr/lms/lib/ajax/service.php?sesskey=9WBF5r6dj1&info=core_course_edit_module 500
send @ jquery-3.5.1.min.js:2
ajax @ jquery-3.5.1.min.js:2
call @ first.js:88
x @ first.js:121
(anonymous) @ first.js:121
dispatch @ jquery-3.5.1.min.js:2
v.handle @ jquery-3.5.1.min.js:2
first.js:11 Uncaught (in promise) TypeError: Cannot create property 'stack' on string ''
at first.js:11
at tryCatch (polyfill.min.js:1)
at Generator.invoke [as _invoke] (polyfill.min.js:1)
at Generator.t.<computed> [as next] (polyfill.min.js:1)
at o (first.js:11)
at f (first.js:11)
at first.js:11
at new Promise (<anonymous>)
at Object.<anonymous> (first.js:11)
at Object.exception (first.js:11)