Is the 4% rule effective for retirement?

Probably not, depending on your health and how long you live. The "4% withdrawal rule" was a ballpark number intended to sustain a 30-year retirement using a diversified/balanced portfolio that earns something close to historical returns.
If you retire at 50, you (or you and spouse/partner, if applicable) could well live another 40-45 years, or even longer depending on your health, longevity in the family genes, and advancements in medical technology.
Most financial assets are currently overpriced due to global central bank monetary policy on steroids. In my view, it's likely we'll see very poor average annual returns (using buy-and-hold) in stocks and bonds over the next 7 to 10 years. Will that pull back average returns over the next 30 years? If you retired today, I think it probably would hurt the longevity of your portfolio.
But portfolio withdrawal strategies are not all that useful if established in a vacuum. They need to be coordinated with other retirement resources that you'll have (and spouse/partner, if applicable). This could include Social Security, possible part-time employment or self-employment while officially retired, any guaranteed income via annuities or pension, other assets such as home equity (if needed), and so on. Most folks benefit from tapping a (genuine) retirement planner to help them with this kind of planning.