I'v used newspaper in the past but have found that mine don't really tear it, they just take the big pieces I put in and use them as is (falling over moltiple times as they make their whay to the nest at the top of the cage lol). I never tried it as bottom liner: I used fleace at the very beginning but didn't like it at all as it was always imediately smelly. Now I use hamp, whitch I am very happy with. I'm thinking I could use newspaper to line the shelvs I sometimes (rarely, as I end up having to wipe them down one or twice a day) put in the cage...I use newspaper. As long as there's not much colored ink. Black is non toxic and my rats looooooove to rip it up, tear it to pieces, shred it into tiny bedding, which is as soft as anything. And.... It's free and plentiful lol. I also line the bottom of the cages with it and just remove one piece at a time to spot clean pee and poops. It makes for fast, easy, clean cage cleaning and rattie cleaning, lol. I still have some bad little ratties that still insist on only using their litter trays until there's some poop in it, then they want a new, clean toilet.
My rats where perfectly litter traind when thay came to me, but have now started to also poop in a plastic box I hang at the top of the cage... they dont poop anywhere else, so I can still consider myself luky, but still, they had me used to other standards