So, there is 2 different questions here that you're asking.

Btc can actually work for you and earn good profit by not doing anything, and that is called holding. May it be a long term hold or mid term hold, depending on your profit range preferences.
I also am in favour for long term hold because you can maximize the profit as Bitcoin tends to be increasing each and every year.

On the other hand, the safest way to store your Btc is using cold wallet. I don't want to store Btc in any custodial wallet  no matter how trusted it is. It would be better to just keep your Btc on a non-custodial wallet like Electrum.