Hello. I see different platform like nexo, blockifi, etc... that can borrow you crypto or stablecoin. I'm here to ask if you have a strategy for example you borrow btc with an interest rate of 6% and then you use it on defi with 8% APR. Thanks for helpful.

Well, the intention is good but you neglect to see 6% interest rate is big enough that could give you some burden when in times of paying the loan. If you can find other platforms that can offer less, that will be fair unlike having this one. Will you have the capacity to pay for this on time?
I hope you'll be thinking this several times. You might be reading that most of us here are not in favor of committing loans just for trading or for investment it is just because we can never have the assurance in crypto. The volatility will affect your profit and that we can't guarantee that we can be profitable all the time so we can make payment as what is the promise.