Canon Photo Software can't access Mac Photos library on external drive

I just downloaded and installed Canon's Digital Photo Professional 4 (DPP4) for Mac. My Mac Photos Library is located on an external Sandisk SSD. Although successfully installed, DPP4 cannot display photos from my Mac Photos Library (my Mac Photos app can do so just fine).

1. DPP4 recognizes the external drive in its folder list and also "sees" the Photos Library located on that external disk in its folder list.
2. The external drive is NOT encrypted.
3. I have given DPP4 Full Disk access.
4. At one point, DPP4 asked me to allow access to Finder, which I did (but it didn't make any difference).
5. I went to Finder settings to see if I could add an extension, but it only displays extensions already installed by various software (such as my Affinity Photo). DPP4 is not listed, nor does there appear any opportunity to add it.
6. DPP4 can display photos if they are located on my Mac Studio's drive (such as the Desktop folder).

Does anyone out there know what privacy or other settings I can try? The folks at Canon couldn't figure it out.

Thanks,

David