According to what I have read on the forum for Portuguese speakers, Duo now is advising against using your photo as an avatar.
As usual, privacy reasons are the pretext. Future releases may ban photos allowing to identify users.
So what is your avatar:
The photo in DL shows me ...
The photo in DL shows me the way I looked 25 or more years ago ...
I am one in the crowd ...
I am (ab)using the photo of a celebrity ...
It's a photo of my pet, didn't you notice?
It refers to my professional activity ...
It refers to my favorite sports or leisure activity ...
OK, my avatar is an owl from a 1970's Dutch comics series for children. I will post some YT videos once I find them.