Their "protections" are FDIC, which is basically a government insurance fund. With regards to Celsius, we don't know if they lost user funds, or if they are having a liquidity crisis. There's more detail here [0], but I think it's certainly possible that they do have user funds and simply cannot handle withdrawals for the majority of their user base all at once despite having the funds (much like a bank).

[0] https://news.ycombinator.com/item?id=31720457