Although a previously undisclosed factor, that clearly influences your desire to find a workable method to directly transfer files between your Mac and iPad, the issue with your ISP internet connection is clearly beyond scope of the technical issue.
You may also need to consider that Apple actively deter attempts to transfer copyright protected media between devices - instead requiring that DRM-protected material is downloaded directly to the target device from its source. For iPad, Apps and associated storage are sandboxed - which can restrict the ability to access or move files between App storage containers, in particular those relating to video or music.
Remember, Finder on Mac will only show your iPad when it is directly connected to the Mac via USB; the iPad will not be visible to Finder via a WiFi network connection.
If you are unable to resolve your difficulties with Finder, you might consider using a third-party utility App - such as iMazing.
A further alternative might be to consider using a File Manager App with your iPad - that can access network shares. A good choice might be Stratopherix FileBrowser - Document Manager, or its “pro version” FileBrowser Professional:
https://apps.apple.com/app/filebrowser-professional/id854618029
https://apps.apple.com/app/filebrowser-document-manager/id364738545
You might review the extensive online Manual and help files to determine suitability for your needs.
https://www.stratospherix.com/products/filebrowserprofessional/filebrowser-professional-user-guide.php