Why is the Keyboard Maestro Macro Editor Slow & Laggy?

[hello]

What is your Mac model, RAM, etc?

Check if you have any large variables (ie variables with a huge amount of content), this macro might help find them:

Listing KM Variables by Descending Size (And Optionally Clearing Some)

A quick piece of JavaScript for Applications: See which variables contain the largest amount of material Optionally select and clear a few variables. Moderator Edit: Macro UPDATED below by author: 2021-02-06 (See, for example, the need to trim down which was reported here: The script below takes a few seconds to display the size-sorted list of KM variables, so if you paste it into (Yosemite+) Script Editor and run it from there, it displays a little progress pie-chart at the bottom…

I've seen the beachball when I try to edit a macro that uses a very large variable.

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also,
try disabling animations:

How to Disable KM GUI Animations

You can disable animation in Keyboard Maestro or Keyboard Maestro Engine with: defaults write com.stairways.keyboardmaestro.engine DisableAnimation -bool YES defaults write com.stairways.keyboardmaestro.editor DisableAnimation -bool YES