Weirdly the OpenTTD Steam page seems to be missing entirely at the moment: https://store.steampowered.com/app/1536610/

Not weirdly, that's the point of the whole announcement. You can't get OpenTTD on its own from Steam anymore, it comes with TTD now https://store.steampowered.com/app/3766810/Transport_Tycoon_...

No, you misread. It's bundled on that page, which links to here:

But the OpenTTD item listed in the bundle is non-existent at the moment.

	▲	haunter 4 hours ago \| parent [-]
		Doesn't matter because you can't buy on its own. It's like a free DLC. https://steamdb.info/bundle/70574/#subs https://steamdb.info/app/1536610/