I have used the Microsoft Remote Desktop app both for iOS and macOS since ages. It was a bit awkward to use on the iPhone, but OK with the iPad. But this was the age of iPad 3, so over ten years ago. I still use it on the Mac and the program is working fine, it is not polished, but I don't see many bugs or issues anymore. I mainly use it for remote connecting to a server.
I feel this is just a "re-imagination" of it, and with support for the cloud based subscriptions. If they will now require a subscription to use it, I will stop using it, and find another solution than Windows Server. Same if they abandon the RDP app. I see from their information that there is a web-version of the Windows App, does it mean to connect to a local machine from a Microsoft-web hosted page, or a version you supposedly installs on your local machine?