So many of my clients have issues with being able to pronate (flat arch) their feet, either one foot or both feet. This is usually due to the misconception that pronation is BAD. Pronation is NOT bad, as long as you are able to control the pronation and move from supination (high arch) to pronation and back to supination. The problem comes when you are STUCK in either pronation or supination. Then there is work to be done.
Often the problem of being stuck in pronation results in being given orthotics to wear. The problem I have with this is that now instead of being STUCK in pronation, you will be STUCK in supination due to the orthotics, neither which are useful to you.
The best way to deal with feet that are STUCK is to reconnect with them and put them through the ranges they were designed to achieve, slowly reminding the brain that it can access these ranges of movement.
The inability to pronate or supinate can have massive negative effects further up the kinetic chain. You definitely want to get assessed and make sure your feet are propelling you through life and not slowing you down!