I'm not sure I fully understand assignment risk

As the title says, I'm not sure I grasp assignment risk. Since I started actively trading a few years ago, I've spent 90% of my time with futures and cash settled indices (SPX, NDX, RUT) with the remainder of positions being single leg options on American style tickers. One of my main strategies now is opening 0 DTE long butterflies on SPX, RUT, or XSP, sometimes symmetrical and other times broken wing. I obviously never have to worry about assignment and managing positions requires very little thinking. I'm thinking about trying to replicate the strategy on more tickers, but I'm confused about how to manage. For instance, if I open a butterfly on QQQ or SPY with 0 DTE expiration, am I at risk of getting assigned if the short legs are ITM before 4 pm?