Yes there is a flicker because your server has to load the scripts. This is coming from the Kirki plugin. You can read about the issue that was opened here: https://github.com/aristath/kirki/issues/1725
And yes the Autoptimize plugin helps because it basically caches it for you so it doesn’t have to load every single time.
When you go into the TotalPress customizer options fro any of the typography controls you will see the following:
Download font-family to server instead of using the Google CDN.
This makes it a little faster.
Hope this helps.