After flashing the phone, it was a tragedy T_T

Today my phone was soft-bricked. The reason was that whenever I tried to install software, it kept prompting that the files were corrupted. None of the apps could be installed. So I had to reset the phone. After resetting, the apps could finally be installed. But I realized, it was a disaster. Now my phone can't even run a single QQ Browser in the background. Pressing the minimize button just causes it to automatically exit. Damn! T_T Two years ago, when I first bought the phone, it could run QQ and QQ Browser in the background while also using Tiantian Dongting to listen to music. But now, not only can I not run QQ Browser and QQ simultaneously in the background, I can't even run QQ Browser in the background at all. Whenever I open QQ Browser, it prompts that there is not enough memory. Damn! This phone has completely turned into a brick. I really want to smash this broken phone! I will definitely never buy a Nokia phone again! Especially the 6120ci! I am a living example! After about a year, it becomes very laggy. Even changing a theme prompts that there is not enough memory. Occasionally it also has black screen crashes. It's simply impossible to run multiple apps in the background simultaneously.