Hello @Kevin Riley ,
You can try and compress the file using Zip or RAR to reduce the size. If the file is still >500MB then try uploading to OneDrive and generate a shareable link and submit this Link in the description details.
You may refer to this similar question: https://answers.microsoft.com/en-us/windows/forum/all/how-to-submit-a-file-for-malware-analysis-that-is/fcc9b9e4-b79f-49ea-aec2-7ca54c0328c8
If this does not work, you can consider creating a support case and uploading the file there.
https://support.microsoft.com/en-us
I hope this helps to answer your question.
If you find the answer above helpful, please Accept the answer to help anyone in the community who might have a similar question to quickly find the solution.