Scammers create accounts that closely mimic a well-known figure or company — matching the name, photo, and even buying fake followers to look credible — and post or comment claiming a limited-time giveaway: "send 0.1 ETH, get 0.2 ETH back".
These often appear as replies under a genuine celebrity's real post (so they ride on that post's real visibility), or are pushed through a hijacked, previously legitimate social media account that's been compromised and repurposed for the scam.
There is no giveaway. Any crypto sent to the listed address is simply gone — the "double your crypto" promise is never fulfilled, and the scam typically disappears or pivots to a new account once reported.