Using Helix you need user interaction if it’s a client-side app, there’s no avoiding that.
If you want to you could use the OAuth flow, redirect to localhost even if you’re not running a webserver there, and copy the token out of the url and paste that into your page (only do this if it’s local HTML/JS/CSS that wont be shared! As you MUST NOT share the token). That’ll last about 60 days after which time the token will expire and you’ll have to do it again.
It’s not ideal but if you’re working within the limitations of a client-side HTML file with no actual server, or app to run on, then you don’t have a lot of options.
The Get Streams endpoint will work Reference | Twitch Developers
Make sure you’re correctly sending the Accept: application/vnd.twitchtv.v5+json header with the request to ensure it’s a v5 request, otherwise it’ll default to v3 which has already been removed (like v5 will in the near future).