I tried resetting my iPhone 8 by selecting "Erase All Content and Settings", but for some reason, when I check my storage after, "Other" is taking up 50GB??? I haven't even backed up any new/old data into the phone, so it should have been in a clean slate. For some reason, "Other" is still taking up 50GB. What's going on?
Try resetting the phone.
Back it up first using iTunes (or the Finder on macOS Catalina.) And don't forget to give the backup a password so it saves your passwords.
Then go into
Settings > General > Reset and erase all content and settings.
This will reset it to factory defaults and delete the caches and temporary files or whatever else is taking up that space.
Then restore the backup you just made and most, if not all, of that "other" storage being taken up should be reduced substantially.
If not you may want to look at
Settings > General > iPhone Storage and see if you have a particular app that is holding on to a lot of storage space.
On rare occasion, erase all content and settings will free this, but most of the time you want to restore it from Finder on a Mac or iTunes on Windows.
The why is space from apps that should be deleted either is stuck or there is file system corruption or snapshots that aren’t cleaning. Normally, this is a small portion of storage and letting the device run, shutting it down once a day for three days cleans things up well. When that is not effective, restore it to factory default - do not sign in to iCloud or restore a backup and then report the space with nothing on the phone.