Late coming to this so you’ve probably already tried. I’ve successfully cut copper sheet, 0.5mm thick, a couple times now.
Using 1.5mm 2 flute upcut bit, (1/16 inch bit worked too). 254mm feed rate, 220 plunge rate, and 0.3mm depth per pass. (10in/min FR, 9in/min PR, and 0.01181in DP)
However, I’d suggest going with a downcut bit or fasten down with double sided tape as the 0.5mm copper is quite flexible and wants to pull up into a full depth cut with the upcut bit unless clamped down really well.
Hope this helps.