You should make a list of the most important conflict points that your character will have to face throughout the book. It's important to be able to tell beforehand roughly which problems your character has to face and overcome - if there is nothing to overcome the character is too powerful and/or you didn't think about the mental component.
There are different sorts of writers out there - those who plan and those who simply write and see what they bring to paper. But in any case it's a good idea to have at least a rough idea of what their characters will go through over the course of their book. This list can of course be updated depending on what you discover about your characters and their world while writing, but it gives you an idea of what you can and should focus on and where your character has too many or not enough weaknesses.
If you are thinking about what you want to write - what are the situations where your character will look powerless?
Just because you are the most powerful being doesn't mean that you are invincible.
For example the Big Bad Evil Guy could simply try to kidnap your friends and family. They are not so powerful, are they? But you are vulnerable because you have feelings that humans could relate to. You want to know your friends and family safe, which is giving your antagonists a leverage they can use.
Or you are the most powerful being - in face-to-face combat. That doesn't mean that a knife in your back during the night won't kill you. Surprises can still surprise you, even if you have a lot of alarms. A real life advice here would be that security is not meant to be perfect - it's meant to be a deterrent that will make the resources your antagonist has to use too high and the costs in case your antagonist fails too grave to make it useful to try to steal something from you.
And while we are at face-to-face combat: how many people does it take to overwhelm you? Three? A dozen? Do you have a powerful mage that can basically control the thoughts of everyone around you? In that case you could define how many are too many to control at the same time.
And people can relate to flaws. Some people might look up to a perfect super powerful being, but others - for example the love interest of your protagonist - might prefer someone who shares a common interest or displays a certain character trait. Being powerful is nice and all, but what about being good with kids/animals/..., eloquent, funny, ...? How can your character show this? And what might happen if they try to and fail? What if the kids start to cry suddenly? Would your character go so far as to use their almighty mind-control abilities on kids or their love interest? That would be a pretty big character flaw and you should definitely think about this.
All in all you should think about the limitations of your characters power. Which aspects can your character not control, when is it too much, what could your character do, but deciced they don't want to do, what do other characters value in a person, ...?
There is more to a protagonist, an antagonist and supporting characters than mere strength. Wits and character flaws are an important aspect of what is means to live. That's why it's important to think about the most important positive and negative aspects of the most important characters before starting your writing. At least a bit - this list will probably get updated regularly and that's fine.
If you only watch out for the problems while writing you will more easily get lost. It's far easier to keep track of your "milestones" that you have defined earlier and to re-read something and see if it aligns with your "character sheet" that states the most important traits and problems than trying to keep an eye on signs for overly powerful characters - because that is pretty open ended and you don't have any criteria to define a find.