Quick summary

The file you selected isn't a Lightroom Classic catalog. Imagen can only upload from a catalog file ending in .lrcat.
 

How to fix this

1. Create a new project in Imagen and click Browse to choose the catalog again.
2. Pick the file that ends in .lrcat. 
   
   Do not pick these files and folders that sit next to it:
     • .lrdata folders (previews)
     • .lrcat-data folders
     • .lock, -wal or -shm files
     • Backup .zip files
    
3. If you can't find the catalog, open it in Lightroom Classic:
     • Mac: Lightroom Classic › Catalog Settings › General › Show
     • Windows: Edit › Catalog Settings › General › Show
     The catalog is usually in Pictures/Lightroom.
    
4. If you only have a backup .zip, unzip it first and choose the .lrcat file inside.