Hey there @Jonathan H.1 - sorry to hear about your downloading issue.
As you noticed, it isn't currently possible to download folders that contain more than 10,000 files or are larger than 20 GB via the web interface. I apologize for any inconvenience this may have caused.
When you need to download a folder larger than this, the best way would be to add the files to your Dropbox and allowing them to download to your computer using the Dropbox desktop application.
Once you click the "Add to my Dropbox" option, these files will be added to your Dropbox account and will immediately begin syncing down to your linked computer(s).
Or else, you'd need to split the original folder into smaller folders.
I hope this clarifies things and please let me know if I can be of further assistance somehow.