To get updates for a manga, you must click the 'Add to Library' button. Once you do this, you will get updates in Updates section of the main site. Also, make sure to leave the bell icon.
To add on @BakedBanana post, Mangadex doesn't have notify -aka ping or show system notification to- you when there is updates on your manga.
So you might be:
checking your titles feed frequently if you checked the bell button (once every hour or so?)
join translator discord server (if any) to get notified once some release comes out.