Apps installed via Flatpak on Pop OS unable to upload, download, import, export, or save files

I'm running Pop!_OS 22.04 LTS (a flavor of Ubuntu), all updates available in the Pop Shop have been installed. Apps installed via flatpak appear to have a permissions issue.

For example--

• Brave: can't import bookmarks

• Calibre: Add books > select file gets message "calibre, version 6.9.0 ERROR: Cannot add books: You do not have permission to read any of the selected files."

• Newsflash: Can't import file containing feeds, freezes when trying to import file

• Element: Can't attach files

• Zoom: Can't attach files in chat

• KeePassXC: Can't add attachments, freezes when tried

• Signal: Can't upload or download attachments, crashes after asking where to save the file.

I've installed Flatseal, but changing its settings has not helped (possibly because it too is a flatpak app). I also reinstalled flatpak. Running the apps from terminal doesn't help. Rebooting has not helped, nor has repairing flatpak.

Any suggestions would be much appreciated. Thank you!