Thanks for the tips, @Shamino. I found the receipts in the same place you did.
After reading the discussion at the above link I am hesitant to disable SIP though, not least because the posts are all previous to macOS 26.
Maybe I am being too cautious?
If something goes wrong, would reinstalling the OS fix it?
[Edit:] I tried deleting the receipts, and they do seem to be protected by SIP.