Hello everyone.
I'll share my experience and how I fixed it.
Quick recap: until recently the connection between my S10e and Windows 10 worked flawlessly - EVEN THOUGH I DID NOT USE IT VERY MUCH. Then something happened and yesterday it stopped working (I could receive phone calls on windows, but could not open the phone's screen or any app within windows.
So I reset everything (purged cache, purged all data on both mobile phone AND PC - I even uninstalled the apps and reinstalled them on both). I could not complete the linking process - and was stuck at 60% (on PC - on the phone it completed the process and was waiting for the final permission).
One thing to note: on my PC when I had to input the microsoft account I was presented with a window with 3 accounts: my personal o365 account, my working account, and a legacy skype account - I was trying to connect with my personal o365 account.
Something had happened recently that broke this functionality - but what was it?
It turns out that recently I started using skype with my legacy account on my laptop with: a user that only has username and no e-mail. I set it years ago and re-spawned recently as I work from home now - and as a matter of fact I get windows notifications that some microsoft account needs to be fixed...
Suddenly I was struck with an idea: could it be that this account needing to be fixed is causing the issue? I removed the skype legacy account from windows settings (win->settings->Account->e-mail and account) and... boom! the app now completed the process!!
I don't know whether this set up is similar to yours (I had an account that was causing troubles with windows as it didn't have an e-mail and it was seemingly causing issues with the app), but if it does I hope it does indeed solve your problem (and maybe other people's too).