I have added backend = systemd and the error i now get is ;
service fail2ban start

• Starting Authentication failure monitor fail2ban
  2024-02-29 14:07:55,591 fail2ban [348]: ERROR No module named 'asynchat'
  2024-02-29 14:08:25,956 fail2ban [347]: ERROR Could not start server. Maybe an old socket file is still present. Try to remove /var/run/fail2ban/fail2ban.sock. If you used fail2ban-client to start the server, adding the -x option will do it

trying fail2ban client -x start also fails.....

I saw mention that i should set backend = systemd but not sure as i'm not using systemd.
I have added backend = systemd ...

Well, if your system does not use journal, then sshd wouldn't log to journal and this setting would be wrong in that case.
You have to ensure where sshd basically logging:

• either to journal (you can also check it with journalctl), then this f2b-backend is correct.
• or to log-file, then find it out in sshd- or rsyslog-settings, and set backend to auto and logpath to proper path to the log-file.

... and the error i now get is :
No module named 'asynchat'

Is python version 3.12+? (see #3487)

Then it is only possible with newer fail2ban version or if you install that modules manually, e. g, with pip as described in pyasynchat and pyasyncore

Otherwise I don't understand why this must be not found within ubuntu 24.04 (no matter container or not).
How you installed fail2ban there? Manually (from source or deb) or from apt?

I had this issue but installing from the .deb in the releases fixed it for me