Hey Mate!
I am associated with the software testing industry but I have never got a chance to work on Microsoft test manager. But considering the fact that you need help to cope up with your needs related to the Microsoft test manager, I would suggest you use various Test & Feedback extension which works in Chrome, Firefox, and will be supported in Edge Chromium once it becomes generally available. However, the idea works only well for the manual testing requirements.
I am sharing this information as I once had a conversation with my friend who was associated with a project based on a Microsoft test manager. In his opinion, there’s no specific replacement for the Microsoft test manager.
In short, you have to rely on different tools and technologies to meet all the defined goals. Meanwhile, I’ll even try reaching out to my friends who can share any detail on this.