I would like to buy a 4iii power meter integrated in a Shimano 105 crank arm.
On my bike I currently have SRAM Apex 1. Will this be possible?
Your question is a little ambiguous but I think you are proposing to replace the Apex non-drive side crank arm with a Shimano 105 arm with a 4iii power meter built in. That will not work, the SRAM and Shimano cranks use a completely different attachment method.
4iii do not seem to offer power meters pre-installed in a new SRAM crank arm, but they do seem to offer to install a power meter unit in a arm you send to them, and list some SRAM options. You could contact them and see what SRAM cranks they can install a meter in, perhaps a Force 11 arm (which I think would be compatible) if they can't do an Apex.
Another option would be to look for whole power meter crank that is compatible with your bottom bracket.