STR:
Paste the following code into a new document and set the language to CSS.

:root
{
	/* --toolbarbutton-inner-padding: 6px !important; */
	/* --arrowpanel-border-radius: 0px !important; */
	/* --panel-border-radius: 0px !important; */
}

.tab-context-line { height: 30px !important;  flex: 1 !important; }

Select lines 3 and 4 (even without 4's EOL).
"Single Line Uncomment".

Result:
Line 5 is wrongly uncommented.
The selection is also wrong.

Notepad++ v8.4.8 (64-bit)
Build time : Jan 20 2023 - 14:41:09
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OS Name : Windows 10 Pro (64-bit)
OS Version : 20H2
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