Is there a way to count characters (each letter, space, & punctuation mark) in a selected text?

There is.

It is an option in the Word Count feature, and doesn't present itself until you have chosen Show Word Count in the View menu.

The Word count appears on the (current) last page of your document, and initially shows the number of 'words' in the document.

Clicking on the up/down symbol to the right of the count offers some options, including a count of all characters used in the document:

Example is from a Pages for Mac document (The topic of discussion in this Pages for Mac community). The process and the feature itself may be different in Pages for the iOS device you list bekow your post. If so, Please copy your question and post it in the iWofk for iOS community.

Regards,

Bsrry

`