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ILb-
No sign of a fix.
It's on a blank screen and is in a loop of playing the startup sound and silent for 15 seconds and repeat... bong... bong... bong...
Internet recovery (option + command + r) hasn't succeeded, that gets stuck in it's own loop of "Enter WiFi details" > downloading, time remaining 0:03 > blank screen > "Enter WiFI details".
Occasionally internet recovery answers with -2100F or something similar, but that's the only exit from the loop it gets in.
If I fire up normally... bong... bong... bong...
Velocio
I upgraded to Big Sur last night.
My 2020 MBP is now bricked.
Am enjoying another day of Apple support.
My hypothesis this time: Does this thing have a BIOS? Did you corrupt it during an OS update?