Office add-in can't be installed on dekstop

Question

so I tried to install this outlook add-in from GitHub https://github.com/pnp/sp-dev-fx-webparts/tree/main/samples/react-save-attachments. I already successfully install this add-in on my outlook web. So I notice on the manifest.xml the source location is like this https://_SharePointTenantUrl_/_layouts/15/outlookhostedapp.aspx?componentId=04634d50-d72c-45ec-81d0-7b1f803800da. First I thought is not working on the desktop because it can't read the SharePointTenantUrl so I change that to my SharePoint address. but when I install it the app still not shows up on my outlook desktop. This is the manifest.xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<OfficeApp xmlns="http://schemas.microsoft.com/office/appforoffice/1.1" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xmlns:bt="http://schemas.microsoft.com/office/officeappbasictypes/1.0" 
  xmlns:mailappor="http://schemas.microsoft.com/office/mailappversionoverrides/1.0" 
  xsi:type="MailApp">
  <Id>04634d50-d72c-45ec-81d0-7b1f803800da</Id>
  <Version>1.0.0.0</Version>
  <ProviderName>SPFx Provider</ProviderName>
  <DefaultLocale>en-US</DefaultLocale>
  <DisplayName DefaultValue="Save Attachments"/>
  <Description DefaultValue="An SPFx Outlook addin that lets users copy email attachments to OneDrive folders."/>
  <IconUrl DefaultValue="https://cdn.graph.office.net/prod/media/shared/addin-icon.png"/>
  <HighResolutionIconUrl DefaultValue="https://cdn.graph.office.net/prod/media/shared/addin-icon.png"/>
  <SupportUrl DefaultValue="https://localhost:4321/help"/>
  <AppDomains>
    <AppDomain>https://login.microsoftonline.com</AppDomain>
    <AppDomain>https://login.windows.net</AppDomain>
  </AppDomains>
  <Hosts>
    <Host Name="Mailbox" />
  </Hosts>
  <Requirements>
    <Sets>
      <Set Name="Mailbox" MinVersion="1.4" />
      <Set Name="SharePointHostedAddin" MinVersion="1.1" />
    </Sets>
  </Requirements>
  <FormSettings>
    <Form xsi:type="ItemRead">
      <DesktopSettings>
        <SourceLocation DefaultValue="https://_SharePointTenantUrl_/_layouts/15/outlookhostedapp.aspx?componentId=04634d50-d72c-45ec-81d0-7b1f803800da"/>
        <RequestedHeight>250</RequestedHeight>
      </DesktopSettings>
    </Form>
  </FormSettings>
  <Permissions>ReadWriteMailbox</Permissions>
  <Rule xsi:type="RuleCollection" Mode="Or">
    <Rule xsi:type="ItemIs" ItemType="Message" FormType="Read" />
  </Rule>
  <DisableEntityHighlighting>false</DisableEntityHighlighting>
  <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides" xsi:type="VersionOverridesV1_0">
    <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides/1.1" xsi:type="VersionOverridesV1_1">
      <Hosts>
        <Host xsi:type="MailHost">
          <DesktopFormFactor>
            <ExtensionPoint xsi:type="MessageReadCommandSurface">
              <OfficeTab id="TabDefault">
                <Group id="msgReadGroup">
                  <Label resid="GroupLabel" />
                  <Control xsi:type="Button" id="msgReadOpenPaneButton">
                    <Label resid="TaskpaneButton.Label" />
                    <Supertip>
                      <Title resid="TaskpaneButton.Label" />
                      <Description resid="TaskpaneButton.Tooltip" />
                    </Supertip>
                    <Icon>
                      <bt:Image size="16" resid="Icon.16x16" />
                      <bt:Image size="32" resid="Icon.32x32" />
                      <bt:Image size="80" resid="Icon.80x80" />
                    </Icon>
                    <Action xsi:type="ShowTaskpane">
                      <SourceLocation resid="Taskpane.Url" />
                    </Action>
                  </Control>
                </Group>
              </OfficeTab>
            </ExtensionPoint>
          </DesktopFormFactor>
        </Host>
      </Hosts>
      <Resources>
        <bt:Images>
          <bt:Image id="Icon.16x16" DefaultValue="https://cdn.graph.office.net/prod/media/shared/addin-icon.png"/>
          <bt:Image id="Icon.32x32" DefaultValue="https://cdn.graph.office.net/prod/media/shared/addin-icon.png"/>
          <bt:Image id="Icon.80x80" DefaultValue="https://cdn.graph.office.net/prod/media/shared/addin-icon.png"/>
        </bt:Images>
        <bt:Urls>
          <bt:Url id="Taskpane.Url" DefaultValue="https://_SharePointTenantUrl_/_layouts/15/outlookhostedapp.aspx?componentId=04634d50-d72c-45ec-81d0-7b1f803800da" />
        </bt:Urls>
        <bt:ShortStrings>
          <bt:String id="GroupLabel" DefaultValue="Add-in groupLabel"/>
          <bt:String id="TaskpaneButton.Label" DefaultValue="Show Taskpane"/>
        </bt:ShortStrings>
        <bt:LongStrings>
          <bt:String id="TaskpaneButton.Tooltip" DefaultValue="Opens taskpane."/>
        </bt:LongStrings>
      </Resources>
    </VersionOverrides>
  </VersionOverrides>
</OfficeApp>

Answer 1

The repo is for SPFx web parts, which must be installed in the SharePoint app catalog.

This repository contains community samples that demonstrate different usage patterns for the SharePoint Framework client-side web parts.

[...]

SharePoint client-side web parts are controls that appear inside a SharePoint page but run locally in the browser. They're the building blocks of pages that appear on a SharePoint site.

Your SharePoint administrator can help you set up an app catalog for the tenant. If you are the SharePoint admin, you may want to refer to https://learn.microsoft.com/en-us/sharepoint/use-app-catalog