I don’t have much experience with Flask but it looks like this example uses Flask on a HuggingFace Space. In Lesson 2 Jeremy goes through deploying a HuggingFace Space app, referencing this blog post the details of which might be out of date but the key takeaway from the blog post for me was using git lfs to upload your model pkl file (one of the export formats you can use to export your model) which are usually large (100 MB+).
You can browse the Show Your Work topic to see some working examples of more recent HF Spaces apps.