What actually happens to crypto getting lost when sent to the wrong address/blockchain ?

Hi, I have a noob question I'd like to ask. If I send crypto to another blockchain (let's say I send 1 BTC to my ETH wallet), the 1 BTC sent will be lost, ok. But what actually happens to this 1 BTC ? Does it get stuck somewhere in the big decentralized cloud of blockchains, waiting to be eventually retrieved by someone smart enough to build a tool that could retrieve it one day ? Or is the 1 BTC simply forever gone, nowhere to be found, and so there is 1 BTC missing in the total marketcap ? Thank you