I use to use a browser extension that would redirect back to old reddit for that. it was very annoying

If you're tapping on the old ui already and trying to tap on links, I've found that if you tap on the 'comments' button, you'll stay in the old ui.

I've been using the 'Old Reddit Redirect' extension in Firefox for a couple of years now.

I don't have to worry about typing old. in front of reddit links, and it bypasses that attempt to redirect to new reddit.