You can't submit forms using a custom visual. A custom visual is hosted in a sandboxed iframe with allow-scripts as the only permission. MS governs this rather than the custom visual author.
If you add an iframe inside a custom visual with your specific permissions, you are asking for a higher privilege than MS has given to the custom visual, and your browser blocks this.
This might be possible by using a PowerApp, but a custom visual (including developing your own from scratch) is not a viable solution for this use case.
Regards,
Daniel