Am I missing something?

[zabadabadoo]

I have not tried this myself, but this post describes use of gnome tweaks to set lid switch setting in Core:

Occasional login loops

CTL ALT F2 to enter terminal. Copy paste the code below into terminal window and hit enter. sudo apt-get install gnome-tweak-tool Launch the app by typing in terminal... gnome-tweaks Find the section under POWER, and under the LID SWITCH setting, tell it to do nothing. Hope this helps.

I don't know what option choices you may be offered by that Power extension.