If you want to switch between Classic and Modern it's now done via a toggle. The advantage of this is that once you've set your preference to the type of view that you want, you should almost always see that view (N.B. there are a handful of exceptions for pages that only work with one of the view styles). If someone sends you a link, it'll now open in the view you prefer, rather than whatever they were viewing it in. The same goes for emails from us.
If you want to switch back to Classic view I've included screenshots below. For those looking to switch, I apologise for the inconvenience, but you should only need to do this once (if it doesn't work, please let me know).
To switch to Classic on desktop, you can find the button under your username:
If you're on mobile you can find the switch at the bottom of the hamburger menu:
Tablets should see the mobile version, so you should be able to follow the process directly above. If you've requested the desktop version on your tablet or mobile you should just need to press your username to get the appropriate dropdown.
We're aware that there are a few bits and pieces of the new nav that could use tidying up, and we're open to suggestions. We'll likely tweak it a bit more in the coming weeks to make sure it works well for everyone.