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Nothing is completely safe, you could put portion of your funds into hardware wallet and rest on exchange for trading. So you don't lose it all.
Regarding secure exchange, I'd stick with binance (cliché, I know). There are also dexes available on popular blockchain platforms where it's not like 'you completely hand over money' which you could use, but they come with their different share of risks.
for those who really want to make long-term investments, keeping your assets in CEX is wrong, saving in a hardware wallet or paper wallet (which you fully control yourself) is absolutely safe.
because dex gives users full wallet access, dex is the best choice to be safe, but the bad thing that often happens to dex is a lack of liquidity (for active traders, they are hated), so most active traders don't like dex and lean more towards cex. indeed, whether it's dex or cex, they still have their own weaknesses, you need to prepare yourself to choose whether you want to trade on dex or cex, besides that, don't underestimate security, always make sure your account is safe.