checkGround.cs

    public CapsuleCollider capCollider;
    
    void Start()
    {
         capColider = this.GetComponent<CapsuleCollider>();
    }

    private bool checkGround()
    {
        //CapsuleColliderの足元に、判定Sphereを設置→Sphere内のオブジェクトを全走査する
        Vector3 sphereCenter = (this.transform.position + capColider.center) - new Vector3(0f, capColider.height / 2f, 0f);
        Collider[] colliders = Physics.OverlapSphere(sphereCenter, capColider.radius-0.2f); //CapsuleColliderより小さくしないと壁に当たっとき着地判定が出る       
        foreach (var col in colliders)
        {
            Debug.Log(col.name);
            return true; //ここでcol.gameObjectなんかを使って適当に判定する
        }

        return false;
    }

    //SphereCenterデバッグ用
    void OnDrawGizmos()
    {
        if (capColider != null)
        {
            Vector3 sphereCenter = (this.transform.position + capColider.center) - new Vector3(0f, capColider.height / 2f, 0f);
            Gizmos.DrawWireSphere(sphereCenter, capColider.radius);
        }
    }