I have tried the following XAML with Arial (Poppins is not installed in my system)

<Grid

xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

<StackPanel>

<TextBlock FontSize="20" FontFamily="Arial" FontWeight="Black">Splendid fireworks</TextBlock>

<TextBlock FontSize="20" FontFamily="Arial" FontWeight="Bold">Splendid fireworks</TextBlock>

<TextBlock FontSize="20" FontFamily="Arial" FontWeight="Regular">Splendid fireworks</TextBlock>

</StackPanel>
</Grid>