Replaced ssd, can’t seem to install OS from my external USB

TLDR; SteamOS won’t reinstall on my new SSD. Konsole opens, runs a few lines, then closes quickly without completing the process.

As the title says, I can’t get the wipe & reinstall to finish. Here’s what I’ve checked so far:

• The new SSD (VIPER VP4000 Mini 500GB M.2 2230 PCIe Gen4 x4 SSD - Solid State Drive - VP4000M500GM23 )shows up in the partition manager, so the Deck does recognize it

• I put the SteamOS recovery image on a 16GB USB stick using the tool recommended on the Steam support page

• Note: the USB stick had ~0.5GB of existing files on it before I flashed it (which I backed up first), not sure if this is causing issues.

Every time I start the reinstall, Konsole opens, executes a few lines, and then just closes, it happens quick, can’t see errors because it closes too fast, no completion, nothing.

Things I’m wondering about:

1. Could the pre-existing files on the USB stick have caused the flash to go wrong? Should I fully wipe and put the recovery img on it again? Would just deleting everything count as a full wipe or do I need to do something else (im on a Macbook).

2. Could the newness of the SSD be causing issues? I can see it in partition manager but haven’t checked whether it’s GPT or something.

3. Is there anything in the recovery process I might be missing? Or anybody had a similar experience?

Any help appreciated: happy to provide more details if needed!