I'd like to know, via email, when a game's news page has a new updated posted to it. Currently I've been checking manually every day, but that's getting pretty tedious. Is there any way to email-subscribe to a game's news? I've checked account preferences and the news page iteself, but I'm not finding any option to do that. I'm already following the game, but I don't get notified through email with new game news.
There is no option I am aware of to mail new news items. However, it is not a new concept that people want to stay up-to-date of changes to... anything... without manually checking a page every time. Therefore, RSS was invented.
You can find an RSS feed of the news items of any game (or at least a lot of games) by using the url
http://steamcommunity.com/games/<game id>/rss/. For Osiris: New Dawn, the game you linked, this would be http://steamcommunity.com/games/402710/rss/. An RSS reader will usually not email you, but if you have one running on your computer it will likely give you a notification that a new news item has been posted. Alternatively, you could perhaps use an online tool that reads an RSS feed and emails you. Suggesting a specific tool is out-of-scope for Arqade though.
(Source: https://bendodson.com/weblog/2016/05/17/fetching-rss-feeds-for-steam-game-updates/, even though the link it crawls for no longer seems to exist on pages)
Use something like https://www.changedetection.com/ to detect when the page changes, and you'll get an email letting you know.