According to a news on Vísir.is (linked below) the magma has started to rise in Fagradalsfjall mountain. At the time of the measurement from a satellite the magma had around 1600 meters (1,6km) left until it reached the surface. At the speed the magma was travelling, around 130 meters a day an eruption was expected to happen around 11-January-2022. This is the current estimate, but that might change of the magma increases or slows down the speed it is going up in the crust.
It is unclear what area is going to erupt since the new dyke is more alongside the older eruption dyke. There is more chance than less that new craters are going to open up and start erupting, some of the area is under fresh lava from earlier eruption. Making the area look interesting when this eruption starts.
Kvikan á uppleið en á enn 1.600 metra eftir (Vísir.is)