Buying one, or multiple ?

Hello investors ! I am a 22 years old man who started investing in ETFs 4 months ago, i live in a third world country where the average salary is 100 - 150$, but i work remotely for a US company for 600$ a month so basically i live like a king here 4 months ago i started investing and buying ETFs, 100$ every month, i bought one ETF which is QQQM, and last month i put a 100$ in VOO My question is, which one is better, buying one ETF and sticking to it, expecting long term return ? (retirement, personal project after 10 to 15 years...etc) or buying a bunch of ETFs which i dont understand wether to put 100$ on a new ETF every month, or divide that 100$ into 3 or 4 ETFs which seems pretty low ?