How many addresses can be generated from a ranged descriptor?

The range is determined by the context, or the caller. As far as the descriptor is concerned, there is no limit (apart from the inherent BIP32 limit of 2³¹ keys); it defines a (practically) infinite list of scriptPubKeys.

The Bitcoin Core wallet, if used in descriptor mode, will dynamically grow the range as keys get used. The lookahead (also called gap limit) is controlled by the -keypool command-line option (or keypool= config file argument), and defaults to 1000. But if say, scriptPubKey number 337 gets used, from that point, the wallet will extend the range to 1337, and consider payments to the scriptPubKeys generated that way beyond 1000 to be its own.

That is however not the only use case for descriptors. For example, Bitcoin Core has a scantxoutset RPC which can be used to sift through the UTXO set for anything paying an output matching a certain descriptor. In that context, there is no notion of a gap limit, as it's just a single shot invocation, and the user can provide the actual range itself.

You can get bonuses upto $100 FREE BONUS when you:
💰 Install these recommended apps:
💲 SocialGood - 100% Crypto Back on Everyday Shopping
💲 xPortal - The DeFi For The Next Billion
💲 CryptoTab Browser - Lightweight, fast, and ready to mine!
💰 Register on these recommended exchanges:
🟡 Binance🟡 Bitfinex🟡 Bitmart🟡 Bittrex🟡 Bitget
🟡 CoinEx🟡 Crypto.com🟡 Gate.io🟡 Huobi🟡 Kucoin.