I have been inside the engine looking at all the settings and fonts then realised I could set this from the project settings
None are set by default.
Then I was directed to the UE50EA fonts.
In the comments, it’s implied that you change the startup fonts from Robo.Small to Robo.Large, but the names do not seem to correspond
loaded font ‘…/…/…/Engine/Content/Slate/Fonts/Roboto-Regular.ttf’ (155K)
loaded font ‘…/…/…/Engine/Content/Slate/Fonts/DroidSansMono.ttf’ (77K)
The full list is
Therefore if you rename Roboto-Medium.ttf to Roboto-Regular.ttf
You increase the size, but it’s just a hack! and you will permanently change the Font to ALL the Unreal processes, but there is no control on the Font size!