Not only that, but you can make it rewrite all reddit links to use old.reddit.com

Yes! Instructions here (old.reddit.com is one of the main examples): https://help.kagi.com/kagi/features/redirects.html

I do the same for Youtube links to Invidious.

Interesting https://invidious.io/

You can also change your Reddit settings to use the old UI for www.reddit.com.

It doesn't work on mobile though.

What do you mean?

Even if you set your preferences to prefer old.reddit.com style, the reddit website will only respect that when accessing from a desktop device. On a mobile device you always get the "new" reddit.

Ohh okay. I skipped a comment in the chain and thought you meant either the redirect on Kagi doesn't work on mobile, or the old.reddit.com site doesn't work on mobile.

Only if you're logged in, though. (I believe?)