cgi is only used for POST/PUT requests handling.

Documentation at https://docs.python.org/3.11/library/cgi.html suggests to have a look in multipart PyPi package at https://pypi.org/project/multipart/:

Deprecated since version 3.11, will be removed in version 3.13: The cgi module is deprecated (see PEP 594 for details and alternatives).

The FieldStorage class can typically be replaced with urllib.parse.parse_qsl() for GET and HEAD requests, and the email.message module or multipart for POST and PUT. Most utility functions have replacements.

Looking at https://github.com/defnull/multipart seems promising:

Features

• Parses multipart/form-data and application/x-www-form-urlencoded.
• Produces useful error messages in 'strict'-mode.
• Gracefully handle uploads of unknown size (missing Content-Length header).
• Fast memory mapped files (io.BytesIO) for small uploads.
• Temporary files on disk for big uploads.
• Memory and disk resource limits to prevent DOS attacks.
• Fixes many shortcomings and bugs of cgi.FieldStorage.
• 100% test coverage.