Yes, Discover cardholders started getting this message last year, but the exact rules have been unclear. For example, I had a message that I couldn't add AUs until December 2020, so I waited patiently for that time frame, and then when I go to add an AU in late December 2020, the message changed to say that I couldn't add AUs until June 2021!
Some people have reported that they were able to circumvent the restriction by calling in to add AUs, but I haven't tried that myself
After reaching 7 AU in 2020, getting my AU access restricted, having my original date extended to January 2021 and placing my card on hold with the old company, I decided to log into my account back in May and discovered (ha) that I could add authorized users online once more.
June rolls around and I receive two AU add notifications. The first AU went through as expected but when I went to add the second AU I was greeted by the maximum authorized users have been added message. I almost gave up and was going to mark the AU as unable to add but recalled recent communication from the old company encouraging me to call in for adds even when receiving that message.
Lo and behold for the second AU I was able to call in and speak with a CSR (probably within five minutes of adding the first AU online). Gave the CSR name/address/dob/ssn, told them I did not want to receive a card at this time and that was it. Two Discover AUs were added in the same month (one online, one via phone). Please try calling in to add Discover authorized users rather than accepting defeat!
As an aside, I suspect Discover is using a rolling 12 month basis and not per calendar year to determine the maximum number of requests to add authorized users. YMMV.