First, take a look at: https://launchpad.net/ubuntu/+archivemirrors
Then, pick a mirror closeby. For example, for me it's: ftp.belnet.be
As such, you can now run:
sudo sed -i "s/archive.ubuntu.com/<your-mirror-here>/" /etc/apt/sources.list && sudo apt update
Still, some network operations may be slow using WSL. You may want to add some exceptions to MS Defender.
Open a new Powershell and run:
Set-ExecutionPolicy -ExecutionPolicy Unrestricted
Afterwards, run the script below (script.ps1) and reset your execution policy if needed:
Set-ExecutionPolicy -ExecutionPolicy Default