Format your Android phone SD card as internal

 I was struggling with my Infinix X671's 64GB ROM being consumed by a lot of apps, their cache and downloads with no way to move them out to the SD card. In comparison to these new Android version (mine being 12), the older ones were much flexible. My 128GB SD card was of no use as I wanted to continue using all these apps that accumulate data on the main internal memory.

The option to format the SD card as internal has been removed in this phone/ Android version. Someone said corrupt the SD card by formatting it using PC as FAT32 or something and then this option comes up. I somehow corrupted the SD card using some tool and this option did show up; however, it was grayed out, meaning I was unable to choose it. The only choice was portable. I was back to square one.

Finally, I found out that adb can help you out. Thats what I did as follows:

1) Enable developer mode. Settings --> About phone --> click build number 7 times.

2) The developer options shows up in the menu now. Click that and enable USB debugging.

3) Find and download USB driver for your phone on your PC or install Google's generic one with their Android Studio (https://developer.android.com/studio). Install the same.

4) Download and unzip the Android SDK tools (https://developer.android.com/tools/releases/platform-tools). Open a powershell in this extracted folder by clicking shift+right click.

5) Connect the USB cable from PC to phone. Set the phone to file transfer or the option other than charging.

6) Allow USB debugging option popping up on the phone. Select "always allow from this computer".

7) "adb devices" should show your device. If adb throws a path error, use .\adb devices.

8) Run .\adb shell and in the shell, run the following three commands:
sm list-disks (to check the id such as "disk:179,0" to be used the command below).
sm set-force-adoptable true
sm partition disk:179,0 private (If you want 25% internal and 75% external, use sm partition disk:179,0 mixed 75%. This latter may take time though)
sm set-force-adoptable false

9) Done, close the shell, unmount USB from PC, remove cable.

10) On the phone, open settings --> storage --> portable --> three dots next to SD card  --> move from internal or something similar. In my case it said 8.1GB will be moved and that it would take 13 minutes. Try it out, if it seems hung up in between like it did for me at 80%, reboot like I did. Retry. Done! Your SD card is now internal.