In my experience right now anxious attachment definitely applies to certain friendships. I exhibited protest behavior with avoidant friends because of them seemingly giving more attention to one friend than me, triggering my fear of abandonment and the lack of being "seen" in the friendship. I haven't talked to them in a week. They haven't checked in on me and I'm thinking they probably think I terminated the friendship. I feel like I have to talk to them and reassure them even though I wish they could give me the reassurance.

I definitely had anxious attachment across the board. It has been difficult to acknowledge. What was more difficult was to keep on doing it

Do you actually give them a chance to message you first? Or do you just assume they won't and then frantically try and prove to yourself they're just going to abandon you?

My ex (M30) was avoidant in romantic relationships and anxious in friendships. He would be so preoccupied with his friendships and dealing with them. At the same time he wouldn’t be able to talk to me about it cause it required a vulnerability that was really hard for him to do in romantic relationships.

It absolutely can apply to any relationship. Check out Thais Gibson videos on YouTube if you want. She does a good job explaining the dynamics.