Cryptocurrencies can be kept online or offline. If the cryptos are kept on the exchange platforms or other online platforms, it can be lost due to hacks.
So it is important to choose the best wallets that are safe and secure. Please help me in choosing the safest cryptocurrency wallets
Whether offline or online, they are still kept or stored in their respective blockchain wallets, that is, ERC 20 tokens are stored on Ethereum blockchain wallets, TRC 20 tokens are stored on Tron blockchain wallets, BEP2 are stored on Binance blockchain wallet and so on. This is why, when depositing a token on any exchange, you will be warned of depositing a wrong token as it will be lost.
Nevertheless, you are right about keeping cryptocurrencies on exchange platforms because they are never secure and the recent Kucoin hack is a clear proof of that. Also, about other online platforms, it is true as well because the creators of that online wallet or platform can easily manipulate everything.
So that brings us to personal wallets, and the best I can recommend is Trust wallet because of its advanced and user-friendly interface. Others are Imtoken, Enjin and Atomic wallet, they are also safe; remember to store your private keys or mnemonic words securely.