The talk around weight loss is kinda crazy and a lot of it is dominated by pseudoscience.
However, we are pretty much positive that eating at a calorie deficit will result in weight loss in 99.9% of cases and you aren’t going to be the 0.1%. There’s a lot of anecdotal data about how eating too little will make you stop losing weight or even gain more weight because of your ‘metabolism’, but no controlled studies that show that to be a significant contributor without other causes. It’s not some magical metabolism trick, you’re just cheating on your metrics and doing less because you’re tired and cranky and have no energy because you aren’t eating right.
Saying that, eating at a massive deficit can definitely make you feel like shit and will make it hard to exercise, do not recommend. You will also likely have a part of your brain dedicated to fantasizing about food 24/7 and your libido will likely be in the trash if that matters to you. This will be very hard to maintain, and you have to remember that there’s never going to be a day where you can go back to eating like ‘normal’. Your current normal is why you need to lose weight and your goal is to eventually establish a new baseline.
Lastly, highly recommend against adding calories back due to exercise. We don’t have a lot of good data about there being any reliable indicators of actual calories burned available to the average person and you’ll find a tremendous amount of super variable answers when you find instances where people tried to actually test the estimates you see online. The time you put into exercise isn’t about weight loss, it will help, but it’s a bonus just for you because you deserve to have the body that you want.