In one account, I have Fidelity premium money market FZDXX. I can see the money market position but the online cash balance includes the amount in FDZXX.
In a different account, I have an FZDXX position. It does not show up in positions but I can see a reinvent dividend on 2/27/26 in the position. Like the other account, the FZDXX position is included in the online cash balance.