Many times they are very similar, especially if you are a walk-in, or need a same day appointment.
The pace may be faster in an E-Room, but not always by much.
One difference, Urgent Care might turn a patient away if they have zero insurance or ability to pay.
I don’t think most E-Rooms could do that.
FWIW, urgent care in my neck of the woods means doc-in-a-box, or a PA at one of the local hospital’s clinics.
I wouldn’t take anyone with difficulty breathing to either.