mail

See the articles Temporarily stop using an email account in Mail on Mac - Apple Support

Take email accounts offline or online in Mail on Mac - Apple Support

If emails appear to be missing in Mail on Mac – Apple Support

Make sure you are not hiding mails ( you have clicked command and L keys ) , again click on view > click on disable message filter .

I do not get this "view" screen. When I press command-L buttons the bookmarks page shows up and "file" button on top left blinks. the view page in top left is the standard one that did not change.

Are you using any anti virus , Unknown softwares / third party apps , cleaners / any VPN services in Mac if so uninstall all of them .

Okay .