In REPO A on project A – yaml files of pipeline (central project for them)
In Repo B on project B – Pipeline tab and code deployment location (IaaC let say).

    pool:
      name: Pool_name

    resources:
      repositories:
      - repository: Repo-A
        endpoint: Endpoint
        name: Project-A/Repo-A
        ref: main
        type: git
        trigger: none
      - repository: Repo-A
        endpoint: Endpoint
        name: Project-B/Repo-B
        ref: main
        type: git
        trigger:
        - main

    stages:
    - stage: stage-1
      displayName: stage-1
      jobs:
      - job: job-1
      displayName: job-1
      steps:
      - checkout: Repo-A
      - checkout: Repo-B
      - script: script-testing

As described in MS documentation, my trigger should work – Define a repositories resource

I have tried to set tiggers, ref’s with different properties but nothing is workig. Configuration
with

    trigger:
      branches:
        include:
        - main

also was tested. Nothing has changed.

What I want to achieve is to trigger this pipeline located in repo A to run when main of Repo-B will be updated.

They are in the same ADO Organization, on different projects. Same endpoint use for both projects.