Activating a credit card is meaningless to FICO
“Activating” a credit card just confirms to the card issuer that you received it. Some issuers won’t allow transactions on the account until that “activation” happens.
Activated or not, a new credit card means a new, OPEN line of credit. It will show on your credit report as an open, active account, and will be accounted for by FICO.
That’s actually no so bad. If you don’t use the card the balance will be zero, which isn’t bad nor good with respect to FICO.
The new CL will be added to the CL of your other cards, which lowers your total utilization. That’s good for FICO.
I would stick it in sock drawer and forget about it.