Nearly any explorer will have close-to-realtime fiat values for your BTC. However, that does typically require the entirety of your balance to be present in a single address (although some explorers do support the use of extended public keys, often with some limitations on the gap limit/number of addresses scanned).
A more comprehensive approach is to import your wallet as a watch-only wallet in an application such as Electrum – this has a couple of benefits over just use an explorer:
- It will automatically track all addresses associated with your wallet, and update as transactions are made
- It supports multiple fiat currency conversions, with multiple exchange rate sources
Of course, many hardware manufacturers also support similar functionality – for instance, both Trezor Suite and Ledger Live allow you to retain a watch-only wallet for your Bitcoin addresses that can be used to track its value and balances even without having the physical device connected.