Steps to reproduce the issue

• Edit templates\cassiopeia\templateDetails.xml
• Line 104 add a close="true" in note field

<field
	name="noteFontScheme"
	type="note"
	close="true"
	description="TPL_CASSIOPEIA_FONT_NOTE_TEXT"
	class="alert alert-warning"
/>

• Go to administrator/index.php?option=com_templates&view=styles
• Open Cassiopeia
• Check alert below field Fonts Scheme
• It has a close button but that doesn't close the alert.
• And (I don't care): The close X should be right aligned. And it has 2 x (1 is a svg background).
• I see the same behaviour in many custom extension settings in the backend where it works without issues in Joomla 3.

<div class="alert alert-warning">
<button type="button" class="btn-close" data-dismiss="alert">×</button>
Some text.
</div>

Additional comments

• No JS errors.
• I tried a lot, using data-bs-dismiss instead of data-dismiss, added alert-dismissible show classes, forced BS loading. No success.