My iPhone 6 is not showing 13.1 update

These are the iPhones and iPod touch models that will support iOS 13, 13.1:

• iPhone XS
• iPhone XS Max
• iPhone XR
• iPhone X
• iPhone 8
• iPhone 8 Plus
• iPhone 7
• iPhone 7 Plus
• iPhone 6s
• iPhone 6s Plus
• iPhone SE
• iPod touch (7th generation)

Yes

That's correct. iPhone 6 is now too old and under powered to run the newest iOS 13 update.

You're welcome.