LIghtroom does not use a folder based system. All imports simply go to the Cloud (and View by Date, etc) where you can place photos into Albums. (Albums can be combined into a 'Folder').
"include sub-folders" TBMK and my experience, photos in sub-folders are automatically included when you select a folder to import, without a checkbox available.
Confirm which app you are using- Lightroom, or Lightroom-Classic ?
Regards. My System: Windows-11, Lightroom-Classic 15.6, Photoshop 27.8, ACR 18.7, Lightroom 9.4, Lr-iOS 10.4.0, Bridge 16.0.3 .