WARNING!
Downgrade Nokia 3.1 Plus is pretty dangerous!
If you didn't make any backup before, you may break your phone!
During partition backup, you'll need to backup following partitions:
proinfo, nvram, nvdata, protect1, protect2 - and most importantly, fdp!
I needn't to mention about proinfo, nvram, protect1 and protect2. Excluding fdp, all these partitions could be recovered by utilizing MTK-SU.
Let me make brief introduce to FDP partition. On Security Patch Level 0x8 based device (you needn't to care about what it means), there's an extra partition called fdp, might related to remote lockdown feature for anti-theft AFAIK(implemented by FIH Mobile, but unused by HMD).
During SP Flash Tool flashing procedure, this partition is easily get broken, so make sure it's backed up before doing any flashing attempt. This partition cannot be reproduced with any known free method or borrowed from other devices, so once it's damaged and you just don't have backup, your phone will stuck at Magenta State (like picture shown below) and now damaged and not recoverable for free. There's some mysterious GSM tool that capable to fix broken FDP but cost a lot, which unsuitable to explain details here.
This is undocumented on source.android.com , definitely something FIH Mobile made themselves. In some cases, it's displayed as " Your device is corrupt. It can't be trusted and please contact support. ".
Besides of that, Nokia 3.1 Plus is not that easy to be downgraded without unlocked bootloader by yourself. To prevent of FRP lock, you should perform regular factory reset at Settings before you downgrade. The only known firmware that acceptable by MTK SP Flash Tool 5.1824 is ROO-2230-0-00WW-B02 on my FIH-Firmware Site. But even that's flashed, the phone still cannot boot properly and will get red state due to system failed dm-verity check when flashed via SP Flash Tool instead of fastboot. However, it could still be possible to boot the phone to recovery and sideload a full OTA. As I don't have bootloader locked Nokia 3.1 Plus right away and limited efforts, cannot write a detailed downgrade guide.
Here's a known full OTA link newer than ROO-2230-0-00WW-B02: https://android.googleapis.com/pack.../0f83ed888b1a5b17d31bb576b9a629d79d097df4.zip
Build version: ROO-225K-0-00WW-B03
Security Patch Level: August 5th, 2019
So, it should be vulnerable to MTK-SU.
Anyone should archive this to somewhere.
Now let's talk about the main topic - internal Android 10 build.
FIH already tested Nokia 3.1 Plus Android 10 internal pretty early (This build for example, October 5th, 2019), but I'm not sure about it's stability. We only made simple test on a Nokia 3.1 Plus TA-1117 (Which is Nokia 3.1 Plus sold in China) and it runs nicely.
Just like Nokia 5.1 Plus, there's no applicable internal OTA packages, instead we only provide full dump. If you don't have unlocked bootloader, you have to install them via MTK-SU leak. The procedure is almost identical to Nokia 5.1 Plus as you'll need to write vbmeta partition individually. As Nokia 3.1 Plus lacks cam_vpu1, cam_vpu2, cam_vpu3 partitions, just ignore errors during flashing cam_vpu1, cam_vpu2, cam_vpu3 partitions.
For some paranoid reason, FIH didn't use 00WW_3_120 as I would expect (they wrote ROO-3120-0-00WW-B02 in systeminfo partition), instead they use 00WW_4_120 in About phone page.
DL: https://www.androidfilehost.com/?fid=4349826312261774372
SHA256: 3140e0ee26f3a23ee479eb4846baaa28a9166c420e76e8e2424a4c223a47682e
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