There's a Firefox add-on that will ensure that you always see the old Reddit, even without logging in.

The problem seems bigger than user hostile UI.

If the company decided to make the UI not friendly, they will likely continue to make user hostile decisions in the name of maximising growth and profits.

In this case using addons seems like playing catch up with low chance of a long term win.

Not on mobile though...

On mobile and non-mobile, I use Firefox' Redirector addon to redirect all reddit links to https://ns.reddit.com/* which might be the same as old.reddit.com

Then download one of the many applications that use reddit's API and enjoy it before they shut down that too.

Well, full support for add-ons is coming to Firefox Nightly for Android soon(ish), at least.

Wouldn’t they know via fingerprinting your device via the device settings or IP?

They could but seeing how good Reddit's UI is, how good do you think their log scraping is? And do they have the budget for keeping all access logs of anonymous users so they can try to line up all the ChainLinkFence enthusiasts with the people who also frequent r/MarijuanaEnthusiasts and r/WhiteMenGoneWild.