Even though I’m not a high-ranked programmer yet, let me share what I’ve learned. Your rating change depends not only on how many problems you solve, but also on how your performance compares to others with similar or higher ratings. If you perform better than expected relative to your current rating, your score goes up; if not, it goes down. Another important factor is the timing of your submissions. In Codeforces contests, solving problems late often means that many other participants have already solved them earlier. Since rating adjustments are based on relative performance, delayed submissions can reduce your standing compared to others, which may cause your rating to drop even if you solved multiple problems correctly.

Maybe because you started solving too late. It is important to start on time and solve problems as fast as possible, so your penalty will not be very big. At 1000-1200 rating, you are expected to solve at least 3-4 problems in div4 contests to improve your rating.

I am leaving Codeforces. if my rating will not reach 700+(current 670) in one month. I solved 2 in div. 4 and -24.

Can't tell the whole process but what I have learnt from my mistakes is that I used to solve a lot problems of 800 level in my early days thinking after getting perfect in it I will move forward. And To be honest it's the worst approach. Am telling you this because you are doing the same. What would be better is to practice some questions at your comfortable level and then move to a higher level. May be initially you have to take help of editorials and solutions but eventually your mind will understand the patterns and soon you will be able to solve at that higher level also. Suppose your rating is X, then solve some easy X-100, your current rated X and upto X+200. If you don't know topic simply learn it side by side, not like first cover whole topic then start problem solving.

Also take help from well known sources like CSES Problem Set for topic wise practice and for learning purposes I will recommend CP-Algorithms this website.

Good Luck ahead :)