There is an extension for it -> https://addons.thunderbird.net/en-US/thunderbird/addon/gmail-conversation-view/ https://addons.thunderbird.net/en-US/thunderbird

There is an extension for it -> https://addons.thunderbird.net/en-US/thunderbird/addon/gmail-conversation-view/ https://addons.thunderbird.net/en-US/thunderbird/addon/gmail... Not super great visually, but works ok