I've not done formal therapy online, but have done crisis chats and emailed back and forth with a residential cener I was considering for treatment at one point. I had a lot of the same difficulties with the written piece. I'm not sure I would be able to do therapy only through writing. It's easier to divulge some things that way, but I would constantly be worried about the emotional context.
Can you bring it up with your online t? I'm guessing there are ways to address all that if they do therapy primarily online...

Is there a specific reason you are choosing online therapy at this time? Were you saying you were weary to try in- person therapy again because of attachment stuff? Or am I mixing that up with someone else? Would you be willing to give in-person a try again? There definitely are challenges with online therapy, mostly the lack of non-verbal cues...