Screenshot thumbnail pops up in the corner and blocks what you're trying to do
Every time you take a screenshot, macOS shows a floating thumbnail preview in the bottom-right corner. It just sits there for a few seconds right on top of your UI, and of course it's always covering exactly the thing you need to click next.
Why does this happen?
This is macOS's floating thumbnail feature introduced in Mojave — it lets you quickly annotate or share the screenshot before it saves. Useful in theory, annoying in practice when you're trying to screenshot-then-click something fast.
How to fix it
To disable it entirely: open Screenshot app (⌘+Shift+5) → Options → uncheck Show Floating Thumbnail.
Or swipe the thumbnail off to the right immediately after taking the screenshot to dismiss it early.
Hold Control while screenshotting (⌃+⌘+Shift+3) to copy to clipboard instead — no thumbnail appears.
Discussion
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