Is the "Xfinity Connect Email" popup window malware?

FYI: I typed a detailed question but when I clicked on a tag my question disappeared. I can't do it again right now but am very worried about the possibility of malware so I'm posting this vague request for help:

I can't get past a "Xfinity Connect Email" popup window (a window I've never seen before) and am unable to see my emails or use my email accounts. Can't even log out properly. 

Is the popup MALWARE?

(Mac desktop, Safari, Sonoma, all up to date, cookies/cache cleared. Window doesn't appear on iPad. Can't find sufficient information in searches to answer this question myself.)