I tried it but I cannot upgrade because error this is my code, check for me please
<?xml version="1.0" encoding="UTF-8"?>
<odoo>
<data>
<template id="my_module_mail_message" inherit_id="mail.Message" name="My Module Mail Message">
<xpath expr="//div[@class='o_Message_date o_Message_headerDate']" position="attributes">
<div class="o_Message_date o_Message_headerDate" t-att-class="{'o-message-selected': isSelected}" t-att-title="datetime">
- <t t-esc="messageView.message.date"/>
</div>
</xpath>
</template>
</data>
</odoo>

I also was add to manifest views/mail_message.xml

Hi, The xml file should not e written in the views, First of all you need to add the xml file in the path your_module_name/static/src/xml/your_filename.xml, Then you need to import this file in manifest like :
'assets': {
'web.assets_backend': [

'your_module_name/static/src/xml/your_filename.xml',
],
},
---------------------------------------------------------------------------------
And in the xml file try adding like:
<templates id="template" xml:space="preserve">
<t t-name="mail.Message" t-inherit="mail.Message" t-inherit-mode="primary" owl="1">
<xpath expr="//small[hasclass('o_Message_headerDate')]" position="replace">
<small class="o_Message_date o_Message_headerDate text-muted opacity-50"
t-att-class="{ 'o-message-selected': messageView.isSelected, 'me-2': !(messageView.isInChatWindowAndIsAlignedRight) }"
t-att-title="messageView.message.datetime">
<t t-esc="messageView.message.date"/>
</small>
</xpath>
</t>
</templates>

Regards.

The error that i get
Traceback (most recent call last):
File "C:\Program Files\Odoo 15\server\odoo\http.py", line 654, in _handle_exception
return super(JsonRequest, self)._handle_exception(exception)
File "C:\Program Files\Odoo 15\server\odoo\http.py", line 301, in _handle_exception
raise exception.with_traceback(None) from new_cause
AssertionError: Element odoo has extra content: data, line 3

To check the issue correctly, can you share the xml screenshot please.

when I follow you, nothing happened, then I tried add to the existing "view" file have error https://drive.google.com/drive/folders/1KcWoHzp3ldM2Z500pnZuRpEDCvbHv2aR?usp=sharing

The mail_message.png and manifest.png files are ok, but you just need to remove the <odoo> and <data> tag from the xml file. Try by removing both.

still nothing happened ToT

Ok I can do that by other way, thanks