Notification delay issue

[Sasa1215]

Because of this issue, I have not received a single notification today from any app except messenger. Can somebody give me a solution?

[أبوسرور١٢٢]

Make sure you didn't put apps in deep sleep mode from Settings  - battery  - limit background usage

Press and hold any apps you want to receive notifications with being delay - exclamation mark - scroll down until you see bat

For Gmail app, you must enable sync option in order to receive the notification instantly