As others have already said, timing can be one of them. How long a player takes before betting can sometimes give you information.
Another thing is betting patterns. It’s not exactly a tell by itself, but if you notice a player plays every hand the same way, using the same bet sizes on every street, it might not tell you exactly what they have. However, you’ll know that regardless of their hand, they tend to play in the same way.
So I’d say timing, bet sizing, and consistency in their betting patterns can still give useful information in
online poker.