You can't possibly grow your Bitcoin without buying Bitcoin, I mean yes you could potentially earn a small interest when you HODL your Bitcoin on some exchange or something like that, but the claim most of the time wasn't really worth it considering the risk you're getting when you HOLD your bitcoin on their platform.

There are some ways you could possibly grow your Bitcoin something like day trading is going to be great if you're into cryptocurrency, but it is risky if you are not updated on crypto. I guess the best way was just to invest in Bitcoin, you could do dollar cost averaging and buy Bitcoin every month or weekly with that you could save Bitcoin and grow it to position for the upcoming Bullrun, that's probably the best way since for sure proven to be a low risk   but you need funds or something like a salary. I mean I wouldn't really recommend gambling at all because it was just too risky and you could easily get addicted to gambling that just means putting your Bitcoin at risk way riskier than just buying or holding your BItcoin.