Cannot get file type associated with the application

I've just posted to the Ultimaker Cura forum, as Cura is the only application in which I seem to be getting this problem. But I suspect this may be a Win 10 issue so hope someone can help please.

Despite having set the defaults correctly, I cannot get d-clicking from File Explorer to open Cura 4.9.1 (the latest version, installed two weeks ago). Same for 4.90. And using 'Open With...' does not work either; I go through the prodedure but when I try 'Open With...' again there is no entry for Cura.

I'm not a programmer but it seems that Win 10 is still trying (but failing) to open an old version, Cura 4.8.0. I base this guess on running SysInternals' Procmon tool. I started it then quickly d-clicked an STL, waited a few seconds (with no Cura opening), then stopped Procmon and filtered the roughly 256K entries by 'Process = Cura.exe' AND 'Path contains Ultimaker'. That gave 78 entries, the first few of which I've pasted below in case this offers a clue to the technically enlightened. ALL 78 entries refer to 4.8.0.

I have Win 10 Version 20H2 (OS Build 19042.1052)
Anyone else seeing this issue with any file type, or able to suggest possible fix please?

--------------------
Time.......................Process....PID.....Operation....Path..................................... ......................................Result......Detail
11:02:25.0527447 Cura.exe 10272 Load Image C:\Program Files\Ultimaker Cura 4.8.0\Cura.exe SUCCESS Image Base: 0x7ff7bfb60000, Image Size: 0x14000 11:02:25.0575370 Cura.exe 10272 CreateFile C:\Program Files\Ultimaker Cura 4.8.0\python35.dll SUCCESS Desired Access: Read Attributes, Disposition: Open, Options: Open Reparse Point, Attributes: n/a, ShareMode: Read, Write, Delete, AllocationSize: n/a, OpenResult: Opened etc
.
.
11:02:25.0580477 Cura.exe 10272 CreateFileMapping C:\Program Files\Ultimaker Cura 4.8.0\python35.dll FILE LOCKED WITH ONLY READERS SyncType: SyncTypeCreateSection, PageProtection:
etc
--------------------

Terry