Like bitcoin is decentralized, same concept. but on exchange of btc / usdt, usd, eur ....
with spot trading, order-book, makers and takers .. and API , WS ..
You will not find a decentralized platform that converts Bitcoin to altcoin except through P2P or using wBTC tokens on the same blockchain.
If you are looking for a centralized platform that does not require KYC, you can look at this list
https://kycnot.me then you can search for API, SW,...