I hear ppl loosing money when migrating from legacy wallets
Don't trust what you "hear", let's verify it with on chain information. If the story has no details on chain, it's can be an AI-written story for fun.
Migrating and selling btc -its not the same ?
With Bitcoin blockchain and non custodial wallet (you have private keys), you can move your bitcoin from one Bitcoin address to other Bitcoin addresses that can be in the same wallet or in other wallets. Other wallets can be yours or can be wallets of someone else.
If you sell your bitcoin, you move your bitcoins to an address in a wallet of another person.
You can move your bitcoin by many purposes, one of them is selling your coins, and other purposes can be consolidate your inputs or change your wallets.
Migrating is not like an accurate term technically. With Bitcoin, we have a technical term "Sweeping"
How to add a Bitcoin address to Electrum / difference sweep and import priv. key