You are entirely wrong.
Actually, a reverse proxy is more complicated than Tailscale. This just shows that you might not know much about Tailscale.
Simply put, all you would do is take the device hosting Channels DVR, click the share button, type in the individual's email that you want to share with, and magically they have access to that device. All they have to do is sign in with their Gmail account with a button, and they magically have a Tailscale account with no effort on their part.
Then, put simply, they insert the IP address from Tailscale as you normally would with Tailscale into their Channels DVR client, and they're done. And you've clicked one button, they've clicked one button, and that's it. If they're using an Apple TV or Android TV device, all they have to do is install Tailscale on that device from the Play Store, App Store, or whatever. It takes all of 10 seconds, and I believe they sign in with a QR code. It's that simple. I have this set up for my mom. It's not hard.
A reverse proxy is simply a worse solution, and without proper authentication, it's more than less secure because it's exposed to the internet effectively, whereas Tailscale is a zero-trust VPN and is significantly more secure. So what you're asking for is a really bad solution as it currently stands.
Lastly, if you want them to only have access to that specific port and only Channels rather than the entire device, you can go ahead and violate Tailscale's terms of service by viewing my post that explains how to set up a Tailscale service, and then go ahead and just simply grant an ACL to that one service, which is simply very easy to do on your part and zero effort on their part.