Adding prebuilt APK to Android system.img (stock firmware from manufacturer)

Can someone help add a prebuilt APK to an Android system.img for me? I’ve obtained boot.img, system.img, etc. (the full firmware) from the manufacturer of the device. I’ve been trying for hours to add the .apk files to the system.img. (I’ll share it here) **My steps:​** 1) What I did was extract the image, add my apk to /app, or /priv-app, or vendor/operator/app. 2) Convert the folders/files of the extracted image to an ISO. 3) Convert the ISO back to .img file using WinISO software 4) Added the system.img converted in step 3 back into the main folder where all the original firmware images are. 5) Flashed the new firmware with the modified system.img back to the device. **Problem:​** The device boots up to the brand logo. However, it just gets stuck at the brand logo. VERY IMPORTANT => If the flash is successful, then the brand logo turns into brand logo animation, but every time I flash with my APK, it just gets stuck at the unanimated boot logo. Thus there are two stages: Boot logo = if stuck, then flashing/APK adding failed Boot Animation = everything works (I know this because the stock flash works just fine) = extra info=​ Android: 4.4.2 Flash tool: MTK SP Flash Tool XDA Forums attachment link: https://xdaforums.com/attachments/mx2-wvga_tm-wv3-22-20230418-rar.6039930/ (The above link is the firmware I was able to obtain from the company)