Would discussing the security of hardware wallets in addition be good or take the warning too far off the point?

Reminder: do not keep your money in online accounts

When you log into a site and it says that you have a balance of "1 BTC" or "1 USD", this does not actually mean that you have that money. Rather, it means that the company showing you this balance owes you that money. In other words, you've given a loan to the exchange. Maybe the exchange will pay you back, but history is littered with defunct exchanges which were widely trusted at the time but ended up not paying back their depositors.

To the greatest extent possible, you should always avoid keeping BTC (or anything else) in online accounts. This is especially important right now because a very large exchange went bankrupt recently, and this may cause a contagion effect which will take down other sites which accept deposits.

Ideally, you should keep your BTC in a wallet where only you control the private keys. Here are some good options:

• For desktops, use Electrum. It also has an Android version.
• For iOS, you can use Bluewallet.
• If you also need to store altcoins, Trust Wallet is a good option.
• If you have a large amount of any coin, store them in a hardware wallet. Reputable hardware wallet vendors include Trezor and Ledger. Do not store large amounts of crypto on an exchange.

Be vigilant - make sure you download the legit wallets and not counterfeit copies of them.

Also, note that many DeFi systems are either fundamentally centralized despite using DeFi tokens/contracts and are therefore about as risky as online wallets, or they are potentially vulnerable to the FTX contagion due to the way that they're designed. Avoid depositing crypto in any service that promises you a monthly or yearly yield, because those services are inherently unstable and are vulnerable to collapse, such as Celsius.

I'm not very familiar with DeFi systems. Should more be said about them?