can i invest 10$ BTC ?

You can invest as much as you want, but obviously, the more you invest, the more you can expect to gain(or lose).
Investing $10 prob. won't make you much. Even if BTC goes up by 4,000 USD, you won't really feel it.

1 BTC = 8,188 USD
0,001221 = 10 USD

If BTC was to reach say 12,000 USD, your 0,001221 BTC would be worth only 15 USD.

If I were you, I'd look into some other crypto.