How do I decide calorie intake and workout balance??

I am 158cm, 61kg 29 year old female. I suffered bulimia and anorexia during my teens and early 20s. I think i must have lost part of my muscle weight during that time. Now I can't get fit because i never had a normal relationship with food. My body is very soft and i feel weak. I cant go to gym currently. I have 3kg dumbells and can buy one more heavier set.

According to some online calculators i must get around 1800 cals to loose weight. Also this gets higher if i workout or even do some walking. It feels too much because i am used to getting around 1000-1200 calories. So i dont know if i should trust those calculators or chatgbt.

Im trying to go over 10.000 steps and consume as much protein as i can. I try to do workout with low weights for 3 times a week using random youtube videos. It would be very helpful if someone suggest some basics about where to start or if im doing something wrong because i keep loose 300-500 gram and then regain them.