One of the fundamental elements of WordPress theming is the ability to create alternative page templates where at the head of the template file you take the standard entry of:

<?php
/**
 * The template for displaying all pages
 *
 * This is the template that displays all pages by default.
 * Please note that this is the WordPress construct of pages
 * and that other 'pages' on your WordPress site may use a
 * different template.
 *
 * @link https://codex.wordpress.org/Template_Hierarchy
 *
 * @package pkresearch
 */

get_header(); ?>

and modify it so as to specify the alternate template name like this:

<?php
/**
 * Template Name:Team Page
 *
 * This is the template that displays all pages by default.
 * Please note that this is the WordPress construct of pages
 * and that other 'pages' on your WordPress site may use a
 * different template.
 *
 * @link https://codex.wordpress.org/Template_Hierarchy
 *
 * @package pkresearch
 */

get_header(); ?>

adding the crucial line of: Template Name: Team Page

as well as naming that new file something like page-team.php

Once upon a time you would need to use a plugin to accomplish the same thing with posts … but for the past several years that is no longer required!

The methodology is very similar where you change the standard head of single.php that reads:

<?php
/**
 * The template for displaying all single posts
 * 
 * 
 * @link https://developer.wordpress.org/themes/basics/template-hierarchy/#single-post
 *
 * @package 346bg
 */
get_header();
?>

and change it to something like this:

<?php
/**
 * The template for displaying all single posts
 * Template Name: alternative
 * Template Post Type: post
 * @link https://developer.wordpress.org/themes/basics/template-hierarchy/#single-post
 *
 * @package 346bg
 */

get_header();
?>

Where the crucial entry consists of two additional lines, the first specifying the template name and the second assigning it to a specific post type

* Template Name: alternative
* Template Post Type: post

and naming the new file something like single-alternative.php

The ability to specify the relevant post type(s) also means that custom post types can have multiple templates!

<?php
/**
 * The template for displaying all single posts
 * Template Name: alternative
 * Template Post Type: artwork_type
 * @link https://developer.wordpress.org/themes/basics/template-hierarchy/#single-post
 *
 * @package 346bg
 */

get_header();
?>

and naming the file something like single-artwork_type-alternative.php

It is worth noting that current developments in Gutenberg and full site editing are introducing templating methodology that can be accomplished via the editor itself