This setting configured the IHttpMaxRequestBodySizeFeature which allow NULL for unlimited. Can you try setting it to NULL? If this has the same issue I'd expect it's likely something set on the server level. Are you on the DXP or self hosting?

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

namespace Microsoft.AspNetCore.Http.Features
{
    /// <summary>
    /// Feature to inspect and modify the maximum request body size for a single request.
    /// </summary>
    public interface IHttpMaxRequestBodySizeFeature
    {
        /// <summary>
        /// Indicates whether <see cref="MaxRequestBodySize"/> is read-only.
        /// If true, this could mean that the request body has already been read from
        /// or that <see cref="IHttpUpgradeFeature.UpgradeAsync"/> was called.
        /// </summary>
        bool IsReadOnly { get; }

        /// <summary>
        /// The maximum allowed size of the current request body in bytes.
        /// When set to null, the maximum request body size is unlimited.
        /// This cannot be modified after the reading the request body has started.
        /// This limit does not affect upgraded connections which are always unlimited.
        /// </summary>
        /// <remarks>
        /// Defaults to the server's global max request body size limit.
        /// </remarks>
        long? MaxRequestBodySize { get; set; }
    }
}

I found this forum thread https://world.optimizely.com/forum/developer-forum/cms-12/thread-container/2022/11/file-size-limit-cms-12/ with some things to try as well. Looks like on DXP there was a blocker coming from Cloudflare in this case, might be worth opening a ticket with Optimizely if your DXP