MS Teams app fails to open in M365 with error "Unable to load requested application. No static tabs are configured."

We have a Microsoft Teams app (manifest v1.20) that provides chat capabilities. The app works correctly in MS Teams Desktop (Version 26072.608.4595.8484) and Web versions. The app also appears in the list of Apps in M365 (https://m365.cloud.microsoft/apps/). However, when trying to access it by clicking on the app name, the following error message is displayed: Unable to load requested application. No static tabs are configured. However, if you go to Apps > All Apps > Get more apps > Built for your org, and click on the same app, it will open the app as a Copilot chat, and will respond to messages. The following updates to the app manifest have been made while trying to resolve the issue:

• removing/changing staticTabs (no impact);
• adding copilotAgents.customEngineAgents field (helped for the app to be opened in Copilot, but not in the M365 app page);
• adding elementRelationshipSet (no impact);
• creating staticTabs with contentUrl and websiteUrl, while adding the domain to validDomains (app crushes in the Microsoft Teams).

Also, a new app was created using the same manifest (staticsTabs removed, copilotAgents.customEngineAgents present). The app can be opened in Copilot chat, but is missing from the M365 App page (therefore, it is impossible to validate the Unable to load requested application. No static tabs are configured. error). What could be the correct solution for the Microsoft Teams app in the M365 web interface to be opened without the Unable to load requested application. No static tabs are configured. error? Attaching a manifest file of the app:

{
  "$schema": "https://developer.microsoft.com/en-us/json-schemas/teams/v1.20/MicrosoftTeams.schema.json",
  "manifestVersion": "1.20",
  "version": "1.1.2",
  "id": "${{TEAMS_APP_ID}}",
  "developer": {
    "name": "Name",
    "websiteUrl": "websiteUrl",
    "privacyUrl": "privacyUrl",
    "termsOfUseUrl": "termsOfUseUrl"
  },
  "icons": {
    "color": "logo.png",
    "outline": "outline.png"
  },
  "name": {
    "short": "short",
    "full": "full"
  },
  "description": {
    "short": "short",
    "full": "full"
  },
  "accentColor": "#FFFFFF",
  "bots": [
    {
      "botId": "${{BOT_ID}}",
      "scopes": [
        "personal"
      ],
      "supportsFiles": false,
      "isNotificationOnly": false,
      "commandLists": []
    }
  ],
  "copilotAgents": {
    "customEngineAgents": [
      {
        "type": "bot",
        "id": "${{BOT_ID}}"
      }
    ]
  },
  "composeExtensions": [],
  "configurableTabs": [],
  "staticTabs": [
      {
        "entityId": "conversations",
        "scopes": [
          "personal"
        ]
      },
      {
        "entityId": "about",
        "scopes": [
          "personal"
        ]
      }
    ],
  "permissions": [
    "identity",
    "messageTeamMembers"
  ],
  "validDomains": []
}