Just for posterity:
I had a “bad” network shortcut (a shell shortcut linking to a QNAP NAS, but for which I had to enter credentials to access) which was causing trouble to File Explorer (in This PC, it was showing the shortcut with a blank icon).
Well, for whatever reason, it was causing the Designer to freeze for a few seconds when I would open a Named Query to view/edit it. After getting rid of the shortcut, the freezing went away.
I’m running on Windows 10 21H2.