I played around a little bit with my own DNS. I can’t get away with a CNAME record because of the security certificate. Other variations haven’t played out well yet.
I am able to mask a site by hosting a simple, single page:
<html>
<head>
<title>Valmetrics Dash App</title>
</head>
<frameset>
<frame src='https://dash-valmx.streamlit.app/?embed=True'>
</frameset>
</html>
The url will remain static on a multipage app, hiding the page urls just fyi. If you can host these couple of lines somewhere that you can control the url more concretely, that would be one solution. Maybe create a page on GitHub? I haven’t hosted any websites on GitHub yet, but it looks like the documentation has options for configuring the url. Azure also lets you host a static web page for free (if you pay for the associated storage) so that’s another option if you happen to already have storage there. I’m sure it’s similar for other cloud providers as well. 