No, In short words 100$ is not enough to start day trade. Again you can start by this amount but you can not earn profit from it except lose. Suppose you start the trade with 100$, how much you want to get profit from it? Basically, for a day trade, we should not expect more than 1-2% per day. So for 100$ 1-2$ per day is enough for you? and you have to mind that there is an exchange fee in this profit. And you can not win every day, sometimes you will lose more than profit. Thus you can lose all of your capital.

For me, even small or large capital in your account, it will not matter. Just RISK MANAGEMENT.

Since, it will also depend on the amount allocated for every position you will enter.
Like 10% of total account balance, or 20% or less/greater than.
You need risk management, you need to plan and stick with it, your target or stop loss.

You can possibly even lose every single time and never earn. If you are a beginner, losing so much can mean you should take a break and learn more, that is probably what’s needed for you to start earning, it’s a winning strategy that is proven to work.
And to answer your question in the OP, “invest only what you can afford to lose”.