I tried to buy a SIM at 7/11 a few minutes ago. TrueMove H, 49 baht.
Was asked for an ORIGINAL passport, I had a copy, which they could keep, but they have a registration process, maybe app-based on their phone where they scan the barcode and take a photo of your passport, so no-go.
Just one 7/11, with just one mini-general manning their post.