\include is really intended for the inclusion of chunks of a document which you might want to compile on their own while working on them e.g. chapters which are part of a book. As such, it is designed for that kind of case and comes with certain restrictions. It should not be used in the preamble, it cannot be nested and so on.
\input is intended to read in files in more generic cases. It cannot be used in the same way to support standalone compilation of document parts, but it is free of the restrictions on
\include e.g. it can be nested.
\input does not write any files to the directory of the included file. This means that you can
\input a file which is not in the working directory or a sub-directory of the working directory without violating the default settings which generally prevent writes to directories above the working directory. Although these settings can be changed, this is not recommended as the setting is designed to mitigate potential security issues.
\input would be both more suitable and more straightforward in this case and will not result in the errors caused by the (mis)use of