Make "Restart later" the default option when the Upgrader currently defaults to "Restart now"
As @anonym wrote on #20105 (comment 231600):
When the IUK has been applied there is a sudden prompt where "Restart now" is default, so users could suddenly have their session shutdown and lose unsaved data.
During the 6.3 cycle I'll check how cheap it is to fix that and if cheap enough, I'll fix it.
cc @sajolida