Bizarre file association problems - Win 10, CC2018 and CS5

I set up a new Dell XPS PC a couple of days ago, with Windows 10 Pro. I installed Photoshop CC2018, and then my old copy of the CS5 Suite Premium (after first deregistering it on my old PC).

I am having huge problems with file associations.  Windows has kindly let me association .psd, .tif/.tiff, .dng and .bmp files with PS CC2018, plus a bunch of other minor formats.

BUT - I cannot association jpegs or raw files with CC2018.  I am able to set CS5 as the default for .jpg files, but only Windows 'Photos' for .jpeg  or .raw format files.

It seems completely random which programs Windows puts in the list I can choose from.  Sometimes there is an option to look for more 'apps', sometimes not.  When there is, if I navigation to my CC2018 Photoshop.exe file and select that, the association stays as CS5. With .raw, there is no option to choose anything other than the Windows Photos app.

Also, if I right-click on any jpg image and select 'open with' the 'choose another app' and navigate to the CC2018 .exe file, it still opens in PS  CS5.

I thought I had won when I discovered that Bridge CC2018 preferences has a 'File Associations' panel.  I dutifully changed every single CS5 association to CC2018 (by selecting its .exe file) but it's made no difference - the files still open in CS5.  If Photoshop CC2018 is open, the files will open in the new program, however, and fortunately clicking on a jpg from within Bridge does also open the file in PS 2018.

I realise others have had similar problems, and I've found an earlier post which gives a registry hack to solve the problem.  Only thing is, the registry entry the hack uses - HKEY_CURRENT_USER\Software\Classes\Applications\Photoshop.exe\shell\open\command - isn't valid for my PC. The only thing listed under Classes\Applications is Opera.exe. There isn't a single other program listed there.

Does anyone have any suggestions re this? Is there another registry entry I can edit?

Under HKEY_CURRENT_USER\Software\Adobe\Photoshop\12.0 the path for CS5 is:

C:\Users\dave\AppData\Roaming\Adobe\Adobe Photoshop CS5\Adobe Photoshop CS5 Settings\

Under HKEY_CURRENT_USER\Software\Adobe\Photoshop\120.0 the path for CC2018 is:

C:\Users\dave\AppData\Roaming\Adobe\Adobe Photoshop CC 2018\Adobe Photoshop CC 2018 Settings\.

Hair being torn out by the minute...