Why does Gamebar need permission to open file explorer?

it's an anti-malware thing, making sure that you intended to do that

You may want to try clearing the MAC address. To do that just go to your network settings, click advanced network settings, alternate MAC address, select clear, then reset. Your console will restart at that point.

Try deleting the app then re downlaoding it, if that dosent work try restarting your xbox by holding the pwoer bitton down until it powers off.

You Tried Reinstall the App and your Console have some free space to make the index?

You can't delete the File Explorer app it's part of the OS. I would try a full power cycle of the Xbox and then try again.