Rampage only shows in the Shader Editor and the Geometry Nodes editor. It does not appear in the Compositor or the Texture node editor. Make sure the sidebar is open with N and look for the "Rampage" tab.

Apply needs somewhere to write. It is disabled when the node tree cannot be edited, which typically means you are looking at a linked material from another .blend file. Linked data cannot be modified.

Save Ramp does not appear at all in factory collections, since they are read-only. Switch to Custom or one of your own collections. If it appears but is greyed out, no Color Ramp is selected. Select one in the node graph.

This is intended. After Apply creates a node, that node stays selected, so a second Apply targets it. Click on empty space to deselect before applying again if you want a separate node.

The preset it pointed at no longer exists. It was deleted or its collection was removed. Click the X on that row to clear it. See Broken favorites above.

Presets live in Blender's configuration folder, which is tied to the Blender version. Installing a new major version of Blender starts with a fresh configuration folder. Blender can copy your previous settings over on first launch; if you skipped that, your presets are still in the older version's config folder.

Rampage is built to never break Blender's interface: a damaged preset file degrades to a message rather than an error. If you see "Rampage: draw error", a preset file may have been edited by hand or corrupted. Open the System Console (Window › Toggle System Console on Windows) for details.