The tags which are in the section title are escaped

[diguage]

The example:

= Example Manual^Alpha^
Doc Writer <doc.writer@example.org>
2014-09-09
:icons: font
:source-highlighter: rouge
:rouge-style: monokai
:stylesdir: assets/styles/
:linkcss:

This is a user manual for an example project.

[#introduction]
== Introduction

This project does something.
We just haven't decided what that is yet.

[#source-code]
== Source `Code` Example

[source,java]
.Java code from project
----
package com.diguage;

/**
 * @author D瓜哥 · https://www.diguage.com/
 */
public class Main {
    public static void main(String[] args)
        System.out.println("Hello, world");
    }
}
----

This page was built by the following command:

 $ mvn

The command:

$ asciidoctor-multipage -v
Asciidoctor Multipage 0.0.16 using Asciidoctor 2.0.17 [https://asciidoctor.org]
Runtime Environment (ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [x86_64-darwin19]) (lc:UTF-8 fs:UTF-8 in:UTF-8 ex:UTF-8)

$ asciidoctor -r asciidoctor-multipage -b multipage_html5 -D . -a toc=left index.adoc

The generated HTML:

<p>↑ Up: <a href="a.html">Example Manual&lt;sup&gt;Alpha&lt;/sup</a>&gt; | Next: <a href="source-code.html">Source &lt;code&gt;Code&lt;/code&gt; Example</a> →</p>

[owenh000]

@diguage, I see the same behavior. Thanks for the report!

(In my opinion, special formatting inside headings is seldom a good style choice. But that's irrelevant.)