No new mail unless I open app and pull to refresh

I have tried k-9 mail numerous time on my different phone past over time, but never get it to work.

Today I installed k9mail on my new Realme X3.
I logged into a yahoo account. And i am not receiving any mail or notification unless i open the app and swipe down to refresh.

Network Sync is set to always.
Background activity of app allowed.
Permissions: Contacts,Read Emails, Delete Emails.

Ver. 5.726

Please help me out.

Did you configure the app to regularly check for new messages?
Account settings > Fetching mail > Folder poll frequency