Have you tried installing a cron daemon in WSL using your distro's package manager and starting it with, e.g.,

  wsl -u root /usr/sbin/service <daemon-name> start

or, equivalently,

  wsl -u root /etc/init.d/<daemon-name> start

Because I've been starting Debian sshd this way using a Windows Task Scheduler "At startup" task for years, in both WSL 1 and WSL 2, and it "just works".

Note that, for my case, WSL 2 requires an additional command to map a TCP port from external adapters to the VM's "host-only" interface, e.g.,

  powershell.exe -NoProfile -NoLogo -Command
    netsh interface portproxy add v4tov4
      listenport=2022 listenaddress=0.0.0.0
      connectport=2022 "connectaddress=$(
        wsl -u root -e perl -e '
          print qq{$1}
            if qx{ip -br addr show eth0}
              =~ m{ ([0-9.]+)/}')"

as a single line, replacing "2022" with the TCP port you want available externally.

>he day I can put things in cron in WSL and have them run without needing a window open is the day I stop running a Linux VM.

You could have already been doing that for years[0].

[0] https://cygwin.com