I had my printer Anycubic-Chiron converted from 1.75 mm filament to 3.00 mm, as it is big enough to handle bigger filament and the printer itself came with two sizes of the heatsink - the other fit to 3.00 mm filament.
In addition, I changed my extruder to a "Bulldog" extruder kit for 1.75 and 3 mm filament plus the PTFE tube and had to change the metal tube (heat break) between the heatsink and the hotend.
However, the conversion failed, the filament gets stuck on multiple points. I found many blogs describing this similar issue. The only possible solution is to increase the heat up to 270 °C at which my printer also fails. As the thickness of 3.00 mm filament prevents the heat to reach the middle of it. That's why it spools on the beginning only of printing then stop. There is no way to continue.
So, the problem is with the hotend, being mostly designed to suit 1.75 mm filament, not the printer itself.