I haven't heard this, may be I was late or something, but can someone explain me what's the risk does he mean? I don't understand, I think bitcoin is yeah like the others having positive and negative sides, usd too, so If saying bitcoin is too risky especially for usd, I don't think so

I think anything is up to you, all of them are depending on you investment plans. If you want to have a passive income by doing nothing, I think staking is the best choices. But remember the coin you staked should have good fundamental and almost stablecoin, why? Of course to keep your asset value, If your coin are getting down yeah in total you'll got nothing.
If you want another business plan, like holding or trading maybe, I think you don't need to stake, it's better if you use your money to be a trading capital