Possible reasons:
Missing Device Support: Your device manufacturer may not support SD Card access.
Use Website Version instead of Play Store Version: Unfortunately, in recent Google Play Store versions, SD Card support was removed due to Google’s restrictions. According to Google, no apps should have access to SD Cards from Nov-21 onwards (see https://rb.gy/mleqvn). Only SD Cards mounted as root can be detected. However, we care about our users’ needs and we have created a separate build of ‘ 
Torrent Pro‘ for users that supports all folders like the previous version. To use this feature, you need to download our app from our official website instead of Google Play Store. Download from https://torrentpro.qinfro.com.