Walking with a significant foot turn out is a symptom of femoral retroversion.
Flat feet are a symptom of femoral retroversion.
With a significant toe turn out when walking flat feet develop or worsen from walking through the arch and not over the ball of the foot.

What is your balance like?
Running?
Femoral retroversion is usually bilateral.
Is on only on your left side or both?
If it is only on the left side hip dysplasia must be ruled out.

This is a rotational deformity of the femur and tibia.
Primary treatment is to attempt to stretch the muscle group in the hip to improve internal rotation.
It is usually corrected in kids when they are learning to walk.
A few episodes to check out.
Episode 230: Squatting With Turned Out Feet? Hey Duck Squatter, IR Yourself.
Episode 249: Improving Hip Extension (And Internal Rotation) for Running
Episode 166: Ninja Recovery and Some Shoulder & Hip Love
Episode 142: Tight IT Band and Hip Flexor Fix: Runners?

SI Joint
Episode 118: SI Area Pain, The Basics
Episode 22: Strong Goats, Orlando Style: Low Back, Hips, and Groin

Flat Feet
Pro Episode #3 – The Flat Feet Solution
Rebuilding Your Feet With Brian MacKenzie
Rebuilding The Feet, Part 2
Rebuilding the feet, part 3

Working on these areas can help improve what you are experiencing.
You don’t know if you can make improvements until you start working on it.
Getting it in the best possible place given the situation.