The user profile setting to hide the left sidebar doesn't completely hide it:
Settings:
"Hide left navigation - When you flip this switch, the left navigation will no longer be pinned to the left of the page on Q&A sites."
It makes it 2/3rds smaller, but doesn't completely remove it. This worked correctly a few months ago.
Reproduced on:
Chrome Android (Desktop view): 108.0.5359.79
Firefox Android (Desktop view): 108.0b6 (Build #2015919115), 77de6a012+