No. Signing up and using the trading journal needs no card at all. You can create an account, import your trades and use the journal permanently without entering payment details.
A card is only needed if you subscribe to Mentor AI, the one paid feature. In that case Stripe collects the card at checkout and charges it immediately, because there is no trial period.
Check your payment method later
After subscribing, you can see the card on file in Settings > Subscription, in the Billing section. For help adding or changing it, see Update payment or card details.