In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- As a Muslim, you should avoid using mandalas or placing them in your home or car.
2- You should replace them with genuine Islamic symbols.
In responding to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
As a Muslim, however, you should avoid using mandalas or placing them in your home or car. By doing so, you are imitating them.
Instead, you should replace them with genuine Islamic symbols. Islamic calligraphy involving verses of the Quran and forms of dhikr and duaa, including the beautiful names of Allah, should be our preferred choices.
So, I would advise you against such mandalas and replace them with the Islamic alternatives.
Almighty Allah knows best.