If you're going to develop mods based on Millennium, here are some important changes Millennium done to Minecraft:
Deprecated, this change will move to Blackbox
net.minecraft.client.gui.FontRenderer fontRenderer in net.minecraft.client.Minecraft
has been replaced by Millennium with extended child class io.github.cleanroommc.millennium.client.font.TextRenderer,
which means there are more modern TextRenderer method implementations,
to use it, cast it into Millennium's TextRenderer first.
It is always safe to cast it into Millennium's TextRenderer.