Please write those who faced this problem. If you found a solution then tell me please how? If you have come to terms with this problem, please also write.
If this is indeed a problem with Moodle and IIS, then the request will be sent to development - https://tracker.moodle.org/browse/MDL-75224
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Upload of file with plus 
character in name (example is 1+.docx), will result in the following error on access:
"Can not find data record in database table resource."
In looking at some other special characters, some are encoded and some are stripped. Plus correctly appears as %2B in the URL generated for access.
This task has already been, but for earlier versions of the moodle (https://tracker.moodle.org/browse/MDL-23567). There was also no solution.
I'm facing the same problem Now
Moodle 4.0.2, IIS 10, PHP 8.0, MariaDB 10.8
<requestFiltering allowDoubleEscaping="true"/>