undo change source option and opaque triangle pointers

[Stumped]

Lightroom Version Number

LRC 9

Operating System

1. macOS 10.13 High Sierra

So the other day I made a little booboo and changed a folder name in finder.... I then noticed all the "?" in LR and then did the relink option. When I opened LR again in folder view I did not notice my folders as like I was working on them previously and panicked and hit something in the edit menu..... Anyhow, I think I figured it out but now notice the "undo change source" option in the edit menu. What is that and what does it mean? Cant seem to find it online.... Also, can someone tell me why some of the arrows next to my folders are greyed out?
Tks much

 

[Califdan]

The undo is just telling you that the last thing you did was to select a different source for which images appear in the grid and filmstrip such as clicking on a different folder or collection. If you use the "undo" (control "z" on windows, what is that on a mac Command Z?) it's what will be undone. So, ignore it.

The grey triangles indicate that there are no sub folders under that folder (or you just launched LR and it's still in the process of checking the folders)

 

[Stumped]

tks much

 

[Philippe Coudé du Foresto]

The grey triangles indicate that there are no sub folders under that folder

I would add : no subfolder known by Lightroom . You might have subfolder in the finder that LR doesn't know about (and therefore doesn't show). I such a case, if the subfolder has to be known by LR (because it contains photo that you want to be cataloged by LR), you can use the "synchronize" command on the parent folder.