Linear and radial mask cursors disappear.

If you forget what the keyboard shortcut is, the menu commands controlling this are on the Tools > Tools Overlay submenu. The Never Show shortcut (H for “hide”) is a toggle so you can press it to cycle between hide/show.

So although the H shortcut is what’s normally taught, you can control edit pin visibility in three ways:

The Show Edit Pins menu on the Toolbar that richardplondon showed

The menu commands on the Tools > Tools Overlay submenu

The keyboard shortcuts for the menu commands

@Philippe T  Press shortcut "H" to toggle the viewing mask's lines and dots.

Hey, @Philippe T. Welcome to the Lightroom Community. I'll need more info to help you figure this out.

Are you working with multiple displays? Has this started to happen since the recent release of Lightroom Classic? 

As primary steps, try this:

• Unplug additional displays & use only the default.
• Go to Lightroom > Preferences > Performance > Use Graphics Processor > Set it to Off if it is on Custom or Auto. If this shows you any differences, please check this article to troubleshoot further: https://adobe.ly/3uYiJo4

Let me know how it goes. 

Thanks!
Sameer K