Seriously?
Windows Phone is long dead and already decomposed. Leave it there.
Microsoft totally lost its mobile market presence - for both consumers and developers. Furthermore, it's not even able to make a decent Android phone that would appeal the mass and support it properly.
No. Just no.
I have no argument with your summary statements -- you are indisputably correct on where things stand as of now. But that doesn't mean Microsoft can't learn from what it did wrong, make changes, and be better. In the world before Windows Phone, Microsoft's successes frequently came from failed launches followed by perseverance and iterations, with each new version fixing the problems with the prior version until they got it right (e.g., Excel taking over from Lotus 1-2-3, Word taking over from WordPerfect, taking over GUI leadership from Mac, Outlook taking over Novell Groupware, Windows Mobile coming from behind Palm to mobile dominance, IE dethroning the seemingly unstoppable Netscape, Xbox 360 trouncing PS3). That was how MS beat all its larger competitors to achieve its various dominant positions, approaching each of those as the smaller upstart.
That approach will work in any area where MS has:
1. The resources to keep iterating until it gets it right
2. Strengths it can leverage to have a novel advantage in a new product area
For mobile, MS has the money to pursue a mobile presence. Three obvious strengths it has that no one else can bring to mobile: MS has the Office install base, IT departments across many enterprises, and Xbox gamers using Gamepass or interested in boosting their Gamerscore (though all of these are fading in importance by the month as MS fails to support them). Further, MS has arguably the best AI backend to produce the most capable mobile device or toolset (whether on top of Android or their own). Therefore, MS has the foundation and resources to prosper in mobile IF IT CHOOSES TO FIGHT FOR THIS SPACE.
Also, MS should not just scrap things and start over when it realizes it's doing something wrong, but merely iterate in small steps of continual improvement: shave off the rough patches and expand on the parts people like so that it doesn't alienate the early adopters with each generation (e.g., the way they kept shooting themselves in the foot by starting over from Windows Phone 7 -> 8 -> 10).
MS lost this space because it threw in the towel rather than doubling down and fixing its prior mistakes via iteration. MS has also NEVER leveraged their strengths properly, which is key to any success like this. Basic corporate strategy training teaches using SWOT analysis -- Strengths, Weaknesses, Opportunities, and Threats to develop a plan. Instead of using that, MS threw some crap against the wall, saw it didn't stick and, per Nadella's "Hit Refresh," shrugged and walked away.
DO NOT HIT REFRESH. ITERATE.