How to quickly get the balance of any bitcoin address? (with no third-party API)
There is no way to enable faster querying for arbitrary addresses than scantxoutset in bitcoind.

Explorers provide this functionality by maintaining a separate database of all addresses and transactions which is optimized for that kind of query. Bitcoin Core, on the other hand, is optimized for consensus related queries, which are largely a hashset lookup for a given input for a transaction.

You could try running something such as ElectrumX, which backs the electrum wallet, or Bitcore, which backs many of Bitpay's wallet and explorer services.