After reading your post again, here is some more info:
Point Clouds are like LiDAR data. Photogrammetry makes very dense clouds, but they cannot penetrate trees and foilage like some LiDAR can. They are more accurate than models when measuring distances and such since the models add triangles to connect the dots so to speak.
Point Clouds come in many different formats but LAS and LAZ are common.
Orthos are your maps. They are rectified meaning that every pixel in the map has a perspective of being viewed from perpendicular from above. This is why in your maps you cannot see the sides of buildings like you can in a pure nadir image with its distortions.
Orthos usually come in tif file type and these georeferenced tifs can be viewed and edited in various software.
DEMs are Digital Elevation Models. These elevation models contain everything, while a DTM Digital Terrain Model will have buildings, trees and other objects removed to give you just the ground/terrain.
They are also georeferenced tif files and work in the same software such as Ortho tifs.
The OBJ file and other files are for your 3D textured model. There are various programs that can open and edit them. Usually people just zip together the OBJ and MTL and send it to Sketchfab.
The tfw file is needed by some programs to define how the tif is georeferenced. Usually though, there is a header on the tif file that defines georeferencing.
ESRI products Arc Map/Pro/Online can work with most of these files and have almost endless possibilites, but also cost money and have a large learning curve.
QGIS is free and does a lot of what ESRI does.
Global Mapper is low cost, easier learning curve and can do pretty much all most people need in terms of drone mapping viewing, editing and GIS generation tasks such as contours.
Pointbox is a free online point cloud viewer that you can easily share point clouds.
If you do buy photogrammetry software make sure you demo all of the popular ones. Agisoft Metashape does some really cool things and can output in far more file types than Pix4D.
An example being you can import free state LiDAR data and make your own DEM with it. Its Cloud Service can offer low cost processing and also low cost sharing of ALL of your data to the tune of $10/month for 100GB of data and the data can come from other sources.
Don't get me wrong, Pix4D is also incredible software, but their superior marketing makes them seem like a far better product, when they are very close in terms of real world testing and performance.