https://wccftech.com/microsoft-windows-file-association/

Earlier this week, some Windows 10 users reported that they were unable to select certain apps as their default choices. The issue was affecting users running the latest Windows 10 October 2018 Update (rollout remains on pause) and the Windows 10 April 2018 Update. Microsoft has now confirmed the latest Windows 10 bug and has said that the company will make the solution available later this month.

As reported earlier, the issue appeared with the release of KB4462919 (Build 17134.345) for version 1803 and KB4464330 (Build 17763.55) for version 1809, which were pushed out on October 9 as Patch Tuesday cumulative updates.