All the battery "saving" before was One UI's aggressive killing off of background (seldom used) apps.
One UI therefore had awful notification management as the app will be forced to sleep, hindering any notification from showing up (Gmail and Microsoft Teams notifications are the worst on One UI). This overrides Google's "Doze" feature that is significantly better at keeping apps awake for notifications and smartly sleeping them.
One UI 2.5 changed that but Samsung hasn't got it right yet. Nothing you can do except the good ol' battery saving "tips".
Visit:
https://dontkillmyapp.com/