OK. On further research, it appears to be that the small arrow is nothing to do with DropBox but means that you haven’t given PhotoLab permission to read those folders.
Go to System Preferences and check the Security and Privacy tab to allow access for PL4
[edit] You may also need to delete the PL database to cause a refresh of the folders you just enabled
As to the missing Pictures folder, you haven’t moved it from its default location have you?
All the things I’ve seen do not necessarily show where your image files reside.
Please do the following
If access rights are granted (as Joanna noted above), things should look similar to this:
Platypus and Joanna thank you your suggestions have worked.
Now how do I get the Pictures folder onto the PL4 sidebar?
Open the Finder and drag the folder that contains your images to the Finder’s sidebar.
DPL’s sidebar “favorites” shows the same thing as your Finder sidebar “favorites” - at least on my Mac
I thank you for your help which appeared to work. I could see the images in Photo Library so I clicked on Customise and they disappeared. I went back to the folder just put in and it says that there are no images.
Also Pictures is already in my Finder sidebar but does not appear in PL4.
It looks like your setup has a serious problem.
PhotoLab related fix (at least it’s worth a try)
quit DPL
delete the following
restart DPL and see what you get
A lot of those files you suggest delete are not there.
Also I have found that I can see and work on an external drive which is connected called “Photograph Backup” and the images do not disappear.
I believe you need to include “Pictures” in the Finder favorites by setting your Finder preferences.
Go to Finder / Preferences / Sidebar, and click in the “Pictures” checkbox under Favorites. Pictures should now appear under Favorites in Finder.
It seem that DxO copies Favorites setting in Finder. If this does not work, try restart your Mac. Hope this will work for you.
Thank you Lars. Pictures is in Finder favourites. Also I have restarted my Computer many times but it does not appear in PL4 sidebar.
You really need to delete your PL database and possibly the cache.
First of all, can you see the Library folder under your home folder in Finder?
If not, you need to select your home folder in the sidebar…
Click on the Show View Menu item on the View menu…
Tick the box that says Show Library folder.
Make sure that PhotoLab is closed then…
… go into the Library folder and delete these three files for the database…
And you might as well delete the cache as well…
You don’t strictly need to delete anything else at this time.
Try all that and restart PhotoLab and let us know what happens then.
Thank you Joanna. I have done all that and I still do not see Pictures in the sidebar. What I have found is that there is stability in the folder that I have pulled into Favourites in the Finder sidebar. So I have concluded that a way around is to pull a folder with the pictures that I wish to process into the Finders Favourite sidebar and then I can work on them.
I thank you all for your endeavours to help me solve my problem.
Au revoir
Can you post a screenshot of your Finder preferences for the sidebar?
Here’s mine
And another of a Finder window with the home folder selected please?
OK for the first screenshot - all seems well there.
But the second screenshot looks nothing like Finder on Catalina. The font is wrong, the icons are wrong and the folders and arrows on the right are not standard to Catalina.
Apart from the fact that your “home” folder hasn’t got the correct little house icon, it also doesn’t contain a folder called Pictures - which is why PhotoLab can’t find it in its Favourites list.
This is how I would expect Catalina’s Finder to look
Although Pictures is showing as being in the Sidebar, it is not showing as a sub-folder of your “home” folder.
What you are showing in these screenshots is that you have a non-standard or customised macOS installation (that may be Big Sur instead of Catalina) and that you have changed the position of system folders, in particular the Pictures folder
Most importantly, where is your real home folder with the house icon?
As well as speaking with you I have had a response from DXO. They advised me that my system should be up to date. So whilst my enquiry started with Catalina I have since updated to Big Sur.
I have not done anything with my Pictures folder or the icons.
I have a MacBook Pro with Big Sur. So I decided to load PL4 onto this machine. it all worked perfectly. I can see the Pictures folder and I have the correct icon.
So how my Desktop got to be the way it is I do not know.
Just out of sheer curiosity, right-click on your Pictures folder and show info to see where it is currently living 
Here’s what it looks like in Big Sur. Note that I’ve dragged the folder of test images (Test Set 03) to the sidebar. DPL will show all things that are visible in the Finder sidebar in the DPL sidebar (only in library view)
A solution has been found. Not perfect but it does enable me to see my pictures in PL4.
I contacted Apple. They identified the fact that my Pictures folder existed but could not make it show up in the user file path; it remained greyed out. The solution they gave me was to delete the Pictures folder and its contents completely and then recreate another Pictures folder with a slightly different name and reload all my images from my most recent backup. It worked.
Thank you everybody for your help in trying to solve my problem.
Pict
Did Apple explain why this happened in the first place?
No they did not. I think they were puzzled.
