You can easily configure Mozilla Thunderbird to display messages from all your email accounts on a single screen. Here's how.

Cross-platform Thunderbird is free, open-source email software for desktop and laptop computers.

The instructions here apply to Thunderbird version 68 but should be similar in other recent versions.

Configure Thunderbird

Open Thunderbird. Click View in the menu bar at the top of the screen. If you don't see a menu bar, press Alt+V to display it. Select Folders from the drop-down menu. Click Unified.

All your email from all your accounts will now be grouped into your Inbox, Archives, and Trash folders, as appropriate.