Steps to reproduce:

1. Go to https://test2.miraheze.org/wiki/Special:ManageWiki/settings

2. Go to "styling".

3. click "Show Popups by default"

4. Save.

Expected results is that after refreshing the page, the box should be ticked.

Actual results is it is not being ticked.

Also reproduced on https://dreamsit.com.br/wiki/ where the issue was first noticed.

This issue seems to have removed settings from that site per T5634#110309.