Like most power meters, 4iiii devices will show a slight overestimation of power when used with oval chainrings. This is because oval rings create variable velocity through the pedal stroke, unlike round rings with constant velocity.
You can expect an overestimation of approximately 1-4%, depending on your chainring's ovality (some commonly induce around a 2% error). While your displayed power might be slightly higher than your actual output (e.g., 255W instead of 250W), the key is your power meter's accuracy and consistency.
If you prefer riding with an oval chainring, there are no functional issues; just be aware your power numbers may be marginally skewed.
Note: 4iiii dual power meters on Shimano cranks are not compatible with aftermarket chainrings from other manufacturers.