Why can’t I download iOS 14.8

Can you post a screenshot, it could reveal why you aren't able to update.

Make sure you:

• Are using a WiFi connection (not a hotspot).

• Have your battery charged at least 50%. Better yet, keep it plugged in during the update.

• Are not using a VPN connection.

• Do not have power save mode turned on.

• Do not have a beta version installed.

• You have at least 6 gigs of storage available.

You can also check out this article for help -

If your iPhone, iPad or iPod touch won’t update

https://support.apple.com/en-gb/HT201435

Because the current version of iOS is 15.0.2, and Apple has never supported downloading or installing older versions of iOS.

Actually, for the first time ever Apple is allowing both 14.8 and 15.0.2 for downloading.