GIMP - very slow to open disk access actions

System: Win 10 Pro, 64. Portable Apps installed on a hard disk, not the system disk.
I have been having this problem for a while, but am not sure when it started. Any function, like File>Open, File>New, File>Save or Save As, etc. that calls for disk access takes a very long time to open the dialog box. I've timed it twice and it's about 2.5 minutes.
I also reinstalled 2.10 Portable. It did not change.
I have tested it in the following ways:

1. Following suggestion by John T Haller in https://portableapps.com/node/61190, which is admittedly a different problem, I tried:
a. D:\PortableApps\PortableApps\GIMPPortable - 2_8\App\gimp\bin\gimp-2.8.exe
- got 2 errors of missing dll, it then started loading plugins, then additional dll missing error. I did an end task in Task Manager
b. D:\PortableApps\PortableApps\GIMPPortable\App\gimp\bin\gimp-2.10.exe
- it opened up in dark theme (I use light) and a not full window (also different from usual). Same issue trying to open a file.
c. D:\PortableApps\PortableApps\GIMPPortable\App\gimp\32\bin\gimp-2.10.exe
- displayed 2 dialogs:
GIMP Message: error parsing menu definitions from image-menu.xml, no such file or directory (showed a path)
GIMP 2.10.18 - new version available on 3.23.20
I closed the dialogs. GIMP did not have menus and the tool icons were missing (showed the icon for missing image). Closed.
2. Standard run as Portable App of GIMP 2.10.18-2.
3. Standard run as Portable App of GIMP 2.8.20 (installed in GIMP-2_8 directory - which was named that before installing 2.10)

Using the standard Portable GIMP does work, but the disk access actions, in terms of getting to the initial dialog are just unacceptably slow.

Any help would be appreciated!