You're not gonna like the answer.....
1. Don't print in white.
The problem is exactly what Ed was saying - it's just about impossible to completely eliminate the little hairs that get picked up when printing PETG....those hairs char on the nozzle and when they get big enough, they fall off into your print.
You can remove the buildup from the nozzle while the machine is printing with the tweezers - takes practice, a steady hand, and a willingness to wreck a print or two.
You can decrease the extrusion multiplier by 0.1. (Use 0.89 instead of 0.90 for example) If you under-extrude a little, it makes less threads. You can also increase your gap by just a hair, about 0.02 mm. Causes less brushing of the previous layer.
But that print looks really
good - you don't have many buildup deposits in it. You're not going to get it much better than that on a 24 hour print.