Android can't view local content after OS upgrade
As pointed out in comment, this is because of Scoped Storage introduced from Android 10.
Before Android 10, any app could read or write any files to external storage (the place where apps store their data), if they requested the READ_EXTERNAL_STORAGE and WRITE_EXTERNAL_STORAGE permissions. Starting from Android 10,apps can only access data created by them and not other app's data or common data like images, downloads etc.
This enhances your privacy and is a good thing. Apps can access only data created by them and if they need access to external storage they need to access it using Storage Access Framework (SAF) . The file manager you are using isn't seeking  permissions through SAF, so it can't read while other file explorers you installed can because they use SAF. Apps like Local Storage may help for using SAF when they don't employ this.

Aside, for those users who are rooted and would like to address the security concerns of apps reading data created by other apps, they can try Storage Isolation Magisk Module or XPrivacyLua
also provides a solution by blocking app read/write access to the SD card completely (using the Privacy.BlockGuardOS.open repo hook) or by limiting access to the app's private directories (/sdcard/Android/data/app-id and others, using the Fif.BlockGuardOS.open repo hook).