We are making some changes in the mobile site to make it more consistent with desktop. This change may impact gadgets/user scripts which add icons to the Minerva skin as it will requires changes to addPortletLink support (T344006) that we can't easily provide backwards compatibility support for at this time. The fix is relatively simple. You can patch your gadgets before this change rolls out by following the instructions here
Is my gadget impacted?
If your gadget shows up here (and has not been patched already) it is impacted:
How do I fix it ?
To address this please update any selectors using pseudo ::before to have the minerva-icon-- prefix.
Example here: https://en.wikipedia.org/w/index.php?title=MediaWiki%3AGadget-dark-mode-toggle-pagestyles.css&diff=1169842920&oldid=1160517217