You aren't eating enough and you are doing too much cardio.
I'm early 40s, 5.6 for context, and can lose weight on 1800 calories and just doing 8k steps a day when I watch my macros (30% protein, 40% carb and 30% fat). I've literally lost 1.8lbs in the last 2 weeks doing this.
Admittedly I am at the start of the diet so expect it to slow down, but essentially my plan is:
3 full body weights sessions x a week at the gym for 1 hour
10k - 12k a day steps
On the gym days as the diet progresses I will add in 1 then 2 cardio sessions (swim most likely).
By lifting heavy you only drop body fat and don't drop muscle tissue which is a premium if you are in your 40s.
I did this when I was 42 - 12 weeks heavy lifting eating in a calorie surplus to build muscle where I gained half a stone, then 10 weeks in a calorie deficit while lifting heavy where I dropped just under half a stone.
The difference was the half stone I lost was entirely body fat. So I looked completely different despite actually being slightly heavier than at the start- I looked like one of those fit people which I never thought would be possible.
Calories (and carbs) are necessary for body processes. If you did nothing all day you might survive on 1200 calories but your body isn't going to let go of any weight and it will slow you down. You can keep going for so long but eventually you break mentally. Whereas if you eat more then you have enough calories for things like digestion, hormone synthesis, growing hair, healthy skin, adequate vitamin and mineral intake.
My advice is to ignore the weight on the scales and focus more on body composition i.e how much muscle mass you have and what your body fat % is.