How to resolve slow mail sending issues with Gmail account on macOS?

When clicking the arrow icon (Send) from within the Apple Mail app, using a Gmail account with the correct server settings, the arrow color will fade and the application will act like it has stalled until finally sending the message after about 20 seconds. 

The Mac OS in use is 15 Sequoia running on a new MacBook Air. The machine migrated from was a MacBook Pro from 2017 using an older OS. The settings and terms are somewhat different between the machines i.e. Preferences in the Mail app are now called Settings. The migration was not 1-1 and server settings from the old machine did not migrate. "Migration Assistant" didn't really do a complete job migrating.

Has anyone seen this issue? Are there more up to date server settings instructions for the new Mac OS and its Mail app?

[Re-Titled by Moderator]

Original Title: Mail slow to send with Gmail account