Additionally, to what was already said, the size of storage is giving in Decimal (1000B based) while after formatting it is often shown in Binary (1024B based), which makes the storage look smaller, which it isn't.
And the most of the storage is coming from software stored in your home, not the OS itself. The OS only occupies around 3.3GB on the 5GB root partition:
/dev/nvme0n1p4 5.0G 3.3G 1.5G 69% /
/dev/nvme0n1p6 230M 41M 173M 19% /var
/dev/nvme0n1p8 466G 115G 351G 25% /home
This is part of the motherboard and can only be changed with specific tools from the manufacturer. Back in the days there was
AMIDEDOS
as a dos tool to change it in AMI Bios. You would need to find out, what tool can be used to change it in your UEFI. However, it's possible that those tools are not available to the public.