Installation questions for an ONEPLUS 12 waffle

[piero]

sorry, i don’t know OnePlus devices…

@piero

you may want or need to flash first an appropriate Stock Vendor Firmware to your device as a sane base :

installation of the Stock Firmware OnePlus

switch back to an “official” OS

• download the ROM : [OnePlus 8 Pro][ROM][OTA][Oxygen OS] Repo of Oxygen OS Builds | XDA Forums
• follow /e/OS to Stock ROM on your smartphone using GNU/Linux - OnePlus Edition
• How To Guide - Unbrick Oneplus Open using Official Flash Tool 5.6.6 in EDL mode. | XDA Forums
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Notes this informations can be outdated, please improve them