Outlook Legacy Mac doesn't display Latin1 & Unicode in Subject from Gmail correctly

[Second version of this post with fewer Latin1 & Unicode characters)

Summary:

Outlook Legacy on Mac is not correctly displaying non-ASCII characters in the subject line, when sent from other mail clients, including Gmail.

From Apple Mail:

Original subject line: Mail to Outlook: Latin1: “®©” Unicode: ✅🚩♻︎

Body: Mail to Outlook: Latin1: “®©” Unicode: ✅🚩♻︎

Displayed by Outlook:

In the message list:

Mail to Outlook: Latin1: ╲®©╡ Unicode: â˛∑›ƒ˚©â˙»ï¸⁄

In the MessageSource:

Subject: Mail to Outlook: Latin1: “®©” Unicode: ✅🚩♻︎

Note that all of the characters in the original subject line display correctly in the message body. Some of the Latin1 characters are displaying correctly in the subject line (in this example the Copyright symbol), but not others, and none of the Unicode symbols.

The same email displays correctly in Gmail. The test email sent directly from Gmail displays the same way in Outlook.

However, when the message is sent FROM Outlook, the subject and body appear correct.

MessageSource:

Subject: Mail FROM Outlook: Latin1: =?UTF-8?B?4oCcwq7CqeKAnQ==?= Unicode:

 =?UTF-8?B?4pyF8J+aqeKZu++4jg==?=

Details:

Using MacOS 13.7,  Outlook Version 16.91 (24111020)

Gmail (Google Workspace) is the email provider. The problem occurs when sending via Gmail directly, or another email client like Apple Mail.

I tested sending an email from outlook.office.com and the problem does not occur! 

Incoming MessageSource: 

Subject:

 =?utf-8?B?T3V0bG9va1dlYiB0byBPdXRsb29rOiBMYXRpbjE6IOKAnMKuwqnigJ0gVW5p?=

 =?utf-8?B?Y29kZTog4pyF8J+aqeKZu++4jg==?=

This problem does not occur when switching to New Outlook, and the incoming messages display correctly from all sources. This leads me to believe it's an Outlook Legacy problem, not a Gmail encoding problem (ie. Legacy is just not supporting the specific subject-line encoding being used by Gmail.)