I switched over to 4.20 to test things out and noticed that my main menu widget which does have a 2 point outline is now creating an outline around the shadow, which is creating a double outline. I reopened my project in 4.18.3 and it is still the same and looking as it should.
The feature was changed since 4.18 because some users requested the effect you were seeing to ensure the shadow looked the same as the outline. Going forward there is an option on the font which will let you choose this behavior yourself. Unfortunately this did not make it into 4.20 but it will be in 4.21.