This allows you to see the charts of all instruments on the app and set price alerts, regardless of the account (e.g. CFD, Invest) you are in. However, you can't trade view-only instruments in the account you're currently in.
💡 Example
You're in your Invest account, where you can only buy stocks and ETFs. You can search for the EUR/USD currency pair and monitor its price via the Invest account, but you won't be able to place an order via this account. You will need to switch to CFD.