【Java SpringBoot】「form」テンプレートがない・アクセスできません。

実現したいこと

アプリケーションを正常にデバッグできるようにしたいです。
自分で調べてみた結果、「form」テンプレートがない又はアクセスできないというエラーであることは分かりました。
しかし、どこに問題があるのかモジュール等を見返しても不明だったため、質問させていただきます。

前提

「Spring Boot2入門」という教材で、POSTの値を表示するアプリケーションを作成しています。
デバッグしたところ、下記エラーが表示され正常に動作することができません。

発生している問題・エラーメッセージ

Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.

Sat Apr 01 12:54:58 GMT+09:00 2023
There was an unexpected error (type=Internal Server Error, status=500).
Error resolving template [form], template might not exist or might not be accessible by any of the configured Template Resolvers
org.thymeleaf.exceptions.TemplateInputException: Error resolving template [form], template might not exist or might not be accessible by any of the configured Template Resolvers
	at org.thymeleaf.engine.TemplateManager.resolveTemplate(TemplateManager.java:869)
	at org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:607)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1103)
	at org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1077)
	at org.thymeleaf.spring6.view.ThymeleafView.renderFragment(ThymeleafView.java:372)
	at org.thymeleaf.spring6.view.ThymeleafView.render(ThymeleafView.java:192)
	at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1415)
	at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1159)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1098)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:974)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1011)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:537)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:631)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:205)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:166)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:115)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:341)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:390)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:894)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1741)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191)
	at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.base/java.lang.Thread.run(Thread.java:833)

該当のソースコード

HomeControllerクラス

package com.example.demo.controller;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;

@Controller
public class HomeController {
	@GetMapping("/")
	public String index() {
		return "form";
	}
	@PostMapping("/confirm")
	public String confirm(@RequestParam String message, Model model) {
		model.addAttribute("message", message);
		return "confirm";
	}
}

form.html

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
	<head>
		<meta charset="UTF-8">
		<title>Title</title>
	</head>
	<body>
		<form th:action="@{/confirm}" method="post">
			<label>
				メッセージ:
				<input type="text" name="message">
			</label>
			<button>送信</button>
		</form>
	</body>
</html>

confirm.html

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
	<head>
		<meta charset="UTF-8">
		<title>Title</title>
	</head>
	<body>
		メッセージ：
		<span th:text="${message}"></span>
	</body>
</html>