Hey there!
Sorry for the troubles.
I do know that at times, updating the software may reveal existing hardware issues, but am assuming since you took it in, then ran all the hardware diagnostics?
(You can also run them yourself, if you haven’t already):
Use Apple Diagnostics to test your Mac
https://support.apple.com/en-us/HT202731
If thats already been done, and checks out fine, and it was truly a clean install:
Was Apple able to escalate the issue for their engineer team to take a look at the logs? If not, I may suggest calling again for this.
Likewise, (If the store got that far with your Mac), were they able to replicate the issue themselves, while they had it?
If not, or, if you didn’t take it in for that, my other questions would be your environment:
Do you have any external devices connected to your Mac regularly?
If so, have you disconnected them systematically to see if one, or the other maybe causing an issue?
Likewise, I know you did a clean install, but had the firmware also been reset? (SMC/NVRAM)?
Those answers may help to shed some light, just hope that it’s not a hardware issue for you, although it very well could be, but usually not.
SMC Reset:
https://support.apple.com/guide/mac-help/if-your-battery-wont-charge-mh29198/mac
NVRAM Reset:
https://support.apple.com/en-us/HT201255
