Why I can’t update my software?

Are you following the steps here: Update your iPhone, iPad, or iPod touch - Apple Support

What model is your phone.

If it’s a “6” (not 6s) or earlier, 12.5.5 is as far as it can update.

It shows in their first post it is an iPhone XR.

Thanks.

Might be helpful if this key info was rendered on iOS device screens. 🤔

True.