I've never lost any unfinished messages due to this. I'm pretty sure Chrome prioritizes tabs where you've typed in text. Link in that other comment suggests that Firefox does something similar: "This is a smart process that avoids unloading tabs that are playing media, using Picture-in-Picture, or WebRTC. For more technical information, see this blog post"
And yeah fuck infinite scroll. I usually interact with such sites via their API or data export. Eg searching my YouTube Likes playlist is impossible on the web because I'd have to spend an hour scrolling before I can Ctrl+F