I'm using Kdenlive 21 recently after not using the tool for awhile (and then on a version probably a couple of years old) and in Clip Monitor "Add Marker" is usually greyed out, as is "Edit Marker". I can only "Add Marker Quickly *". However, sometimes I've been able to do the "Add Marker" and put comments in as I've been used to for years. I don't know what I'm doing differently to get the different behavior.

Also, as someone else noted, in the Project Monitor I used to be able to right-click on a clip and "Go To Marker" in which I could pick the named marker and get right to it, but now I have to just scroll and hunt which is very inefficient.

If there's some new workflow to do this I haven't learned it yet.

Save, reload project or even restarting kdenlive may help - that is what I do when experiencint this and other kdenlive hickups (the other day it decided to look all desaturated, ui as well as clips, for some reason, for example).

The "Go to marker" menu in the context menu is working here (21.04.3)

Alt + arrow will move to next snap point, in clip monitor those are markers, in/out-point and clip ends.