As WSL2 uses EXT4 in VHD volume, the VHDs size can grow in time as one uses the WSL. Deleting files isn’t enough and one has to zero-out the free blocks and run the VHD compaction.
From WSL2 console:
mount /dev/sdb -o remount,ro
zerofree -v /dev/sdb
From the Windows host’s Admin powershell:
# Install the HyperV management and powershell optional features
wsl --shutdown
Import-Module -Name Hyper-v
Optimize-VHD -Mode Full -Verbose $env:LOCALAPPDATA\Packages\$((Get-AppxPackage *Ubuntu*).PackageFamilyName)\LocalState\ext4.vhdx