It's allegedly impossible, due to the A/B update mode. Yet it managed to end up bricked, so the question is how, and what can be done.
After investigation (you can do it very simply by looking at the USB ids), it's currently in Qualcomm EDL firehose mode: this is likely due to a failed attempted update https://xdaforums.com/t/fix-pixel-3-qusb_bulk_cid-xxxx_sn-xx...: "because the bootloader has been corrupted during an attempted update - it's in EDL mode because there's nothing else it can boot into. I'd speculate it has some link with that "clever" new approach of being able to update the OS in the background and switch to it on the next boot"
The "clever approach" that causes the problem is called the FOTA (or OTA, for "Over The Air") update, done by the carrier. This is known and documented on https://issuetracker.google.com/issues/248340373
To leave EDL mode, it needs to be fed a bootloader + an image matching its model, to flash the eMMC memory inside.
On Windows, it's easy to do Qualcomm Flash tool (GPST/QFIL) , which is easily available from many places like https://github.com/stanislawrogasik/Pixel5-VoLTE-VoWiFi/tree..., and the process is documented on sites like https://imobiefix.com/qualcomm-prog-emmc-firehose/
Ideally, the MBN file has to exactly match the model, brand (etc) so if you have a 5a, you need a 5a MBN (and maybe a XML file, still reading)
According to https://support.google.com/fi/thread/227549262/sm7520-or-sdm... the model SM7520 or SDM765 ; this is confirmed by https://github.com/hoplik/Firehose-Finder/blob/master/ForFil... because it's listed as a "Snapdragon 765G" / 0011E0E1
According to https://xdaforums.com/t/bricked-google-pixel-4a-5g-mbn-file-... "Google does not make QPST files available for the Pixel series" but someone else might have uploaded that somewhere
Based on https://discuss.grapheneos.org/d/9656-brick-5a-help it's a well known problem: "The Pixel 5A has some hardware issues. I had mine poop out on me recently. Contact Googles repair team. If you have warranty they will replace it" : It's described extensively on https://suspiciouslygeneric.com/2022/11/11/the-hidden-flaw-k...
According to https://xdaforums.com/t/ipsa-pixel-5a-extended-warranty-i.46... "Due to the Pixel 5a Black Screen of Death issue, Google has extended the warranty on 5a devices for one year beyond the original device warranty"
However, google has denied the extended warranty, even while clearly being the cause of death of the phone.
Shame on you google, for creating more e-waste by refusing to release the QPST. If anyone reading this works at google, try to do something. It's not nice to put perfectly usable phones in a landfill just because a QPST is not released.
I hope someone will leak the QPST, because for people who don't have the money, it's also serious expense.