If you just want to track the balance and transaction history for a specific XRPL account, you can add a read only account.
If you want to keep your private keys completely air gapped (offline) but still want to track the balance(s) for an account and check the transaction history, you can add a the public account address (starting with a lower case "r") to XUMM.
Read Only accounts in XUMM (accounts imported by r...-address, without importing a secret key / mnemonic / Secret Numbers) can NOT be used to sign transactions.
You will not be able to sign transactions and requests for read only accounts.
Please note: adding the public account address (starting with a lower case "r") of an exchange does not allow you to track your virtual exchange balance by destination tag! There is no use in adding an exchange / shared address as a read only account.