I think Boyce and Floyd don't count since they officially retired. I'm guessing. Not 100% sure what is going on with D. Brown and Mpagi's scholarships counting towards the 85 limit.
When you look at this roster table from IT:
https://insidetexas.com/football/football.php?pg=fb_roster
It shows 85 players, but that is not including Tarik Black or Jahdae Barron. That takes it to 87. As I stated above, that table includes 5 walkon's and 4 players retired or on medical. My guess, is that Floyd, Brown, Boyce, and Mpagi were moved off or to a medical ship. Not sure how those are counted or not counted towards the 85 limit.