I no longer commute as I WFH, but the coldest I remember was -8 a year or two back and it was nearly all on main roads, so minimal risk of ice.
I remember that!
It was more than a year or two back though, it must have been 2018 - I was still at the Exhibition Centre.
I remember popping into the local shop before riding to work, the shopkeeper said it was -8.
Of course I still rode to work, on my ice bike.
I don't generally feel cold on the bike, because my bikes are heavy, I don't wear thin cycling gear or cycling shoes.
I wear general outdoor clothing, fleeces and similar, topped up with an
Altura Night Vision jacket, a wool beanie, a buff and gloves.
The only times I felt cold in he cold lol, was when in a beginners group, lots of starting and stopping, the pace slower than I would have liked.