I suggest contacting support directly.
Batuhan Birol Keskin said:
I rolled back to Oreo via beta labs OTA however, it can't be updated to December security patch. Why could it be?
How can nokia 8 android 9 downgrade android 8.1 please reply
Hi @manu cm,
You need to get the Android 8.1 firmware from somewhere (e.g. here: https://fih-firmware.hikaricalyx.com/hmd_en.html) and follow instructions on how to flash it, e.g. from the XDA Nokia 8 forum.
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