The UI update from a few minutes ago appears to have removed the hot questions tab of the StackExchange dropdown on the top menu bar from all pages except the Stack Exchange homepage. Instead all I have is "Explore our sites"; which is an apparent replacement for the all sites tab on the old interface. I maybe used all sites once a month looking for an appropriate site for something. Hot questions is my primary interface to Stack Exchange and which I normally visit by just reusing an existing SE tab; now appears to be consigned to a page that I find useless forcing me to keep a browser tab open for no reason other than to avoid the current UI regression.
As a workaround, you can always visit:
And that will give you the equivalent hot question listing that you're missing.
They are sorted by "hotness points" in descending order (hottest first) and you can see exact score by hovering each question's title, e.g.
The list on each site's sidebar just takes the top 12 from this full list.