Why is there an unknown/unauthorized transfer in my wallet?

There are two possibilities behind it:

● Your Recovery phrase is somehow exposed or leaked, and someone who has access to it is stealing the funds from your address.

● You have authorized malicious and scam DApps, which could steal funds from your wallet. When we interact with a DApp, it needs to sign and approve wallet access to these smart contracts.

Malicious DApps could embed malicious codes and gain high-level access to your wallet through the authorization process. In that case, the malicious DApp could drain your wallet through smart contract engagements.

In the meantime, you are encouraged to study and research how a DApp (decentralized App) works and the potential risks of a smart contract/DApp. This can help to avoid the above risks to your crypto funds. Here is an article for example on the CoinMarket platform addressing this topic.