I've done several over the years. Some close to lease end, one a year out and 2 that were 19 months out. Go into your account on the BMW site to get your lease buy out value. This will just be a number on a line that starts at your initial purchase price and meanders on down to your residual value at lease end. Then, like others have said, research the approximate value of your car. Miles are going to be the biggest factor. If you are driving at your lease allowance, the car value and the buyout might be fairly close. But many other factors come in to play, depending on supply, interest rates, demand and for awhile, covid.
You may be in a position to squeeze out some equity because your car is worth more (due to low miles) than the value of where it would be on the depreciation line. If you buy it, you still have to deal with how you will dispose of it. If it's just going to go back to the dealer when you get the new car, they will offer you trade-in value. You might as well just negotiate that value at the time you are negotiating on the new price and skip the buy out. It's all the same. The difference will just be a credit or debit off the new car MSRP. I got a Carmax offer once that was about $4,000 below my lease buy-out - I was at nearly three years worth of miles at 26 months. I got the dealer to buy it out at a higher price. I took a loss there, but got $14,000 off MSRP at the other end on the new car. I had to fly out of state to get it - oh, darn - road trip. A couple of local dealers were only offering between $5,000 and $8,500 off MSRP. My airfare was six bucks using miles. No brainer.
Another time I was offered more than the car should be valued based on the depreciation curve - and I was way over miles at 17 months. The used market was tight at the time. The extra amount I got was about equal to the cost of the Competition option on an M5 and I was able to trade from a Base to an LCI Comp, wipe out 22,000 miles and keep my payment just about the same.
You win some and you lose some. Know your options, know your numbers, know their numbers. If you win great. Savor it. If you're going to lose, how much is it worth it to you? In other words, how bad do you want the car? We've all been there. In the end, if you really really want it and you over pay a few thousand - but it ends up in your garage, you won't care by the end of the week.
Good luck