3d8 force is a lot of damage to be able to call on at once. For instance cantrips at lvl 4 do a max of 1d12 (Toll the Dead), and this feat appears to be accessible to all classes. So... If my fighter who is level 4 chooses this for its feat than it can now do more damage than the party's wizard.

My recommendation is to either raise the minimum level or lower the damage. Also perhaps consider adding a limit to the number of times this can be used per long/short rest. 

Or come to think of it this would make an interesting Epic Boon

So you can turn invisible as an action, gain resistance to force damage (always or while invisible?). Also the damage is very strong with 3d8 on 150 ft.

It has a lot of flavor, but for level 4+ it's way too strong. Limit the uses per long rest or day. Invisibility is a 2nd level spell after all and this feat doesn't seem to limit it's duration and it requires no concentration. Additionally you gain resistance to force damage. Like Darfo99 already mentioned, it's a fun epic boon, but even then I would limit it's uses probably