You just said web though, right? Not the app. There’s downloaders for everything if you have a link to a public post.
“Snapchat video downloader” search gives me an entire page of downloaders. I don’t use Snapchat so I can’t comment on what works or doesn’t, but this is how I download any other social media video.
Hm, still might be worth a shot. There are ways to grab private posts when you’re logged in by using a browser console and finding the line for the video but I’m kinda too dumb for that. I’d probably just use a screen recorder at that point. I don’t need a Snapchat web-dl.