Updated to KB2003_11_C.21, ripped out the boot img patched with magisk and uploaded to the phone.
However unsure if its a quirk as i went from OOS11 to OOS12 the signal keeps just dropping out completely, fixes itself when rebooted but absolutely not sure what the issue is as yet. Semi annoying.
I can upload the boot image clean and patched (unsure if any information is inside it)
yeah, i have this signal loss issue since 2 years - so not oos12 specific