There's no fixed cutoff, but 50x and above is particularly risky since it can be liquidated by nothing more than crypto's ordinary daily volatility (2-5%). That said, the real risk is set by position sizing, not the multiplier itself.
Regardless of the notional multiplier, use position sizing so a stop-out only costs 1-2% of your account, and always check that your liquidation price sits comfortably beyond your stop-loss.