Here's how to disable Siri's new floating button

[pdfu]

When Siri AI is enabled, macOS 27 adds a contextual "lightweight UI" when you type or select text. The floating button can expand into Ask Siri, Edit with Siri and Writing tools, or other contextual actions.

To disable it, run the following command in the Terminal:

sudo mkdir -p /Library/Preferences/FeatureFlags/Domain && \
sudo defaults write /Library/Preferences/FeatureFlags/Domain/WritingTools LightweightUI_macOS -dict Enabled -bool false

and restart your Mac. To restore:

sudo defaults delete /Library/Preferences/FeatureFlags/Domain/WritingTools LightweightUI_macOS

 

[Line_Noise]

This thing breaks layout in so many places it's not funny. Pops up over other controls

 

[MacGizmo]

If you use Adobe InDesign, the Siri button is the same nuisance as ID's "Text Adornment" icon that pops up at the absolute worst possible locations and makes it quite difficult to work around.