Fitness

Just my opinion but I would level it out a bit, you don't need that large a surplus to feel good for your workout, maybe just no deficit wednesday and 250 cal thursday.

Do you workout every day? And do you do just strength or also cardio?

20g carbs per day while doing sports is very low. It is possible your glycogen stores are depleting and making it harder for your muscles to keep working throughout your workout. So maybe also increase carbs on the days around your workout.

Finally, also eat slightly more just after your workout so your body feels it can put energy into muscle growth.

Maintaining strength with such a large deficit will always be super difficult, and remember that also weight moves weight, so don't compare your pbs in weight as you shed pounds but in percentage bodyweight. The first weeks will be the toughest as your body adapts. Good luck!

For your main quetion - yes. Daily calorie deficits basically matter not at all. What matters is the deficit over weeks or months or years.

And yes, being in a calorie deficit will typically result in weaker lifts.

However, the bigger factor at play here is almost certainly the low carbs. Carbs are the main way your body supplies your muscles with glycogen and without that, your lifts will typically go down. The vast majority of bodybuilding research suggests that carbs are good for muscle growth and maintenance. There is some emerging science and some anecdotal evidence that low carb diets can work in a hypertrophy context - but my take is that it may be good during a cut (so good for you), it probably isn't ideal for bulking.

But there are a few things to know about low carbing. First is that there is an adaptation period where your body must learn to run on fat as fuel rather than carbs. During this period, expect basically all your metrics to go down, especially aerobic and glycolytic work. Adaptation, depending on the person, tends to take 2-8 weeks. Also note that you should either be paying close attention to getting enough electrolytes in your diet, or else supplementing electrolytes, as electrolyte depletion is a big driver of the "keto flu". Another thing to note about low carb is that it still follows the biggest rule in weight loss - it only works as long as you keep doing it. If you lose 100 lbs on low carb, then start eating carbs again, you will gain back 100lbs, if not more. If you want to have regular, large cut and bulk cycles, maybe this is ideal for you. But if your main objective is to achieve and maintain a healthy bodyweight, then you will either need to stick to your low carb diet for the rest of your life, or else have some sort of tapering period where you reintroduce carbs but pay a lot of attention to fat gain - which will likely be extremely difficult. For most people, a far more sustainable solution is to build up the weight maintenance habits during the weight loss process. That way you practice the habits until they are effortless, and the weight will just fall off. A final note about low carb - most people recommend that during your adaptation period, you don't restrict calories. Just eat to satiety with low carb meals. You'll lose a ton of water weight anyway, and it isnt unlikely that you will eat below maintenance just based on satiety. Honestly, if you are low carbing, I would recommend just eating yo satiety forever until you stall out on the scale. After all, why kill yourself when you are already headed in the right direction? Anyway, not restricting calories makes it easier on the body and mind to get through the adaptation period, so you should probably do it.

On the topic of low carb lifting again - while some report no change (or even an increase) in their numbers after the adaptation period, most people will see a noticeable drop in glycolytic lifts. Aka, bodybuilding style lifting in the 5-20 rep range where you might get a pump. After all, the glycolytic system requires glycogen, which comes from carbs. But in the low rep range (<5), little glycogen is used, so these lifts are often unaffected. And in the high rep range, you go fully aerobic, which can be fueled by ketones just as well as glycogen.

Reading your post, I feel like my main concern is that you are likely highly motivated right now, and are just throwing everything at the wall - but weight loss is a marathon, not a sprint, and so if your motivation flags, you will end up burnt out and regaining the weight you lost. I would argue for celebrating your win with the overhead press, and getting on a diet plan that will allow you to maintain that standard easily. The best weight loss idea I've ever heard was to just write down everything you eat - not quantity, not calories, just what it is. Because becoming aware of what you are actually eating is often literally all ot takes to start the weight loss process.

You are 6 days into keto (<20g carbs per day). It takes about 3 months to become fully fat adapted. During that time your lifts will suffer a bit.

However, I don't think a calorie deficit is necessary when your already doing keto, if you have fat to burn you won't be as hungry and stop eating early anyway.

Just to sidestep a bit, why do you want to prioritize this lift over losing weight which can be argued to be more important for health?