If this is something you’re planning on checking for a lot, I would make two box components and place them in your capsule so that they occupy the space the character would take if standing from crouch or prone. When the input to stand is pressed, get the component, get all overlapping actors of that component (make sure you set the collision so it only overlaps with level geometry or whatever else you’re checking for), get the length of that array, and if it’s equal to zero, allow the player to stand. I use a similar method to determine if my character can run on walls.
Here’s my blueprint as an example. I check if there IS something overlapping, you would want to do everything the same EXCEPT for the > operator, you would probably want to to an = operator and compare the length of the array to 0.
After you have something like this, just use the return value into an if statement every time the player goes to do the movement.
Some considerations for doing it this way: Your level needs to be made up of static meshes with “generate overlap events” ticked off. This won’t work on BSPs because they don’t generate overlap events.
Let me know if I lost you at any point.