Plat Pro, Platinum, and Gold are upgrade-eligible too but only for certain fare classes.
From
https://viewfromthewing.com/american...ocal-upgrades/ :
Executive Platinum and Concierge Key: at the time of booking
Platinum Pro and Platinum: at time of booking if not buying the cheapest fares (so, if booked into Y, B, H, K, M, L, V, S or N fare buckets) or within 72 hours of travel on lower fare classes.
Gold: at time of booking on full fare (Y, B, H) or within 48 hours of travel