Message Filters dysfunctional for PointCloud2 sensor messages

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I understand the title is vague, but then so is the documentation for message filters. I should say the documentation is clear on method signatures, but at compile time, those signatures are not recognized. Here is a snippet of code:

#include <ros/ros.h>
#include <pcl_ros/point_cloud.h>
#include <pcl/point_types.h>
#include <pcl_conversions/pcl_conversions.h>
#include <pcl_ros/transforms.h>
#include <sensor_msgs/PointCloud2.h>
#include <opencv2/opencv.hpp>
#include <geometry_msgs/PointStamped.h>
#include <tf2_ros/transform_listener.h>
#include <tf2_ros/message_filter.h>
#include <message_filters/subscriber.h>
#include <tf2_geometry_msgs/tf2_geometry_msgs.h> 

using namespace std;
using namespace sensor_msgs;

tf2_ros::TransformListener tf2_listener;

ros::NodeHandle nh;
message_filters::Subscriber<sensor_msgs::PointCloud2> cloud2_sub(nh, "lidar/points", 100);
tf2_ros::MessageFilter<sensor_msgs::PointCloud2> tf2_filter(cloud2_sub, tf2_listener, "camera_odom_frame", 100);

I have tried declaring and initializing the Subscriber and MessageFilter types separately, but the error is consistently:

175:70: error: ‘nh’ is not a type
     message_filters::Subscriber<sensor_msgs::PointCloud2> cloud2_sub(nh, "/lidar/points", 100);
                                                                      ^~
175:74: error: expected identifier before string constant
     message_filters::Subscriber<sensor_msgs::PointCloud2> cloud2_sub(nh, "/lidar/points", 100);
                                                                          ^~~~~~~~~~~~~
175:74: error: expected ‘,’ or ‘...’ before string constant

176:65: error: ‘cloud2_sub’ is not a type
     tf2_ros::MessageFilter<sensor_msgs::PointCloud2> tf2_filter(cloud2_sub, tf2_listener, "camera_odom_frame", 100);
                                                                 ^~~~~~~~~~
176:77: error: ‘tf2_listener’ is not a type
     tf2_ros::MessageFilter<sensor_msgs::PointCloud2> tf2_filter(cloud2_sub, tf2_listener, "camera_odom_frame", 100);
                                                                             ^~~~~~~~~~~~
176:91: error: expected identifier before string constant
     tf2_ros::MessageFilter<sensor_msgs::PointCloud2> tf2_filter(cloud2_sub, tf2_listener, "camera_odom_frame", 100)

I have been looking over the WIki documentation for days and scouring code. Literally everywhere, you can find these very same code snippets and signatures --- but clearly, something has changed in Noetic, and neither the documentation nor other references are accurately reflecting the source code.

Why might it not be possible to use sensor messages with TF2 message filters? What has changed in Noetic that makes the above code invalid? Even the error messages make no sense --- "expected identifier before string constant" and then pointing to the topic. And "nh is not a type"? It's defined as Nodehandle type and pulling from the ros.h header. What could be more obvious to the compiler than that? Honestly, this is borderline ridiculous. Such code worked perfectly fine in Melodic.

ENVIRONMENT:

Ubuntu 20.04 ROS Noetic