Unity MonoBehaviour code for XY/YZ planer circular movement of an object.

CircularMotionXY.cs

using UnityEngine;

public class CircularMotionXY: MonoBehaviour
{
    [SerializeField, Range(0, 1000)] private float _Speed;
    [SerializeField, Range(1, 100)] private float _Radius;
    [SerializeField] private Transform _Center;
    private float _theta = 0.0f;
    
    void Update()
    {
        if (_theta >= 360.0f) _theta = 0.0f;
        _theta += _Speed * Time.deltaTime;
        var theta = Mathf.Deg2Rad * _theta;
        var x = _Radius * Mathf.Cos(theta) + _Center.position.x;
        var y = _Radius * Mathf.Sin(theta) + _Center.position.y;
        var z = transform.position.z;
        transform.position = new Vector3(x, y, z);
    }
    
    void OnDrawGizmos()
    {
        Gizmos.color = Color.red;
        Gizmos.DrawWireSphere(_Center.position, _Radius);
    }
}

CircularMotionYZ.cs

using UnityEngine;

public class CircularMotionYZ : MonoBehaviour
{
    [SerializeField, Range(0, 1000)] private float _Speed;
    [SerializeField, Range(1, 100)] private float _Radius;
    [SerializeField] private Transform _Center;
    private float _theta = 0.0f;

    void Update()
    {
        if (_theta >= 360.0f) _theta = 0.0f;
        _theta += _Speed * Time.deltaTime;
        var theta = Mathf.Deg2Rad * _theta;
        var x = transform.position.x;
        var y = _Radius * Mathf.Sin(theta) + _Center.position.y;
        var z = _Radius * Mathf.Cos(theta) + _Center.position.z;
        transform.position = new Vector3(x, y, z);
    }

    void OnDrawGizmos()
    {
        Gizmos.color = Color.green;
        Gizmos.DrawWireSphere(_Center.position, _Radius);
    }
}