The Arduino IDE developers are tracking this bug here:
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As sterretje, the trivial workaround of doing a "restore" operation followed by a "maximize" operation on the window restores the IDE from this bad state. In case that is not clear, I'll provide instructions you can follow:
Click the "restore" icon at the top right corner of the Arduino IDE window:
Click the "maximize" icon at the top right corner of the Arduino IDE window:
Thanks, it's on MacOS so not the same but yes, I can resolve it. Just another issue with IDE 2 that seems to get in the way. This and the bug with not responding during an upload (and unable to cancel) are two that really kill the flow of working on IDE 2.