This. This is all it is, and it can be fairly simple or really complicated depending on how much you want to overthink it, or whether you have a realistic handle on your yearly costs and spending.
I've posted this before, but I think it was a long time ago. There are other calculators you can find online with more complex variables, but IMHO this'll get you in the ballpark to answer for yourself "what's the number":
https://firecalc.com/
Personally, I believe a 2.5% withdrawal rate is extremely conservative - - so much so that it produces either a 100% guaranteed success rate if you are able to achieve The Number, or produces The Number that is so large that you never get there.
My personal calculations are based on a lightly modified 4% rule and a couple layers of variables / fallbacks if needed.