Limit the Maximum Upload Size

Caps the size of files that can be uploaded through WordPress at 8 MB, even if the server allows more.

Code

add_filter( 'upload_size_limit', function ( $bytes ) {
    return min( (int) $bytes, 8 * MB_IN_BYTES );
} );

This can only lower the server limit, not raise it.

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Use snippet above adds it from the library in one click. Or copy the code into a new snippet with the same code type.
It is added inactive: review the code and settings, then switch it on.