SharePoint Open with Explorer problem and copy problem

I need to move multiple libraries containing SharePoint PDFs to a new location outside of SharePoint and to a new application that will store all files. A quick way to proceed is to use Robocopy to copy a library from the URI (Open with Explorer) provided by SharePoint. 2 of the 3 main libraries that I'm trying to do, fail by clicking the "Open with Explorer" button. Within these 2 libraries, most of their directories have more than 50k articles and I assume that it stops running when you try to load all those files into the explorer.

I tried to change the registry key of my local machine Web client and added FileAttributesLimitInBytes: value 20000000 (error: You can not access a WebDAV Web folder from a Windows client computer), restarted the services, but this did not help to load these directories. Should the registry key be changed on the server where the files are hosted? Or is there anything else I could do to access these pdf to copy it?

In addition, another problem that I encounter is that most files larger than 60 KB are corrupted. For whatever reason, robocopy from the command line / E / MIR / CopyAll does not copy files from subfolders unless the file is directly declared in the command line. I have therefore created an array with all the subfolder names to loop and run robocopy for each subfolder in order to copy their files. However, this process is extremely slow. Each folder contains well over 2500 files, but only about 700 to 900 files are copied, but that takes on average 16 minutes. Ideas for which this process is so slow?