Sometimes you need to allow Clipboard read access in browser in the site:
Are you copying and pasting the actions in same flow? If not are you doing it in the same environment?
The new designer can be sometimes buggy too. When you copy in the new designer it should show in the top right corner text "Copied!":
And you can paste the action to what ever text editor to see that it actually copied the action to your clipboard.
I would try switching to the old designer both when you are copying the action and pasting it.
If you are copying actions from different environment the old designer might not show you the action you have copied but if you press Ctrl + v in this view:
It will show give you the option to paste the action:
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