I was able to successfully follow the steps at https://xdaforums.com/t/how-to-use-an-esim-from-a-different-carrier-on-your-phone-and-watch-galaxy-watch-5-pro-aus-use-case.4571761/ to add a Woolworths Mobile esim to my wife’s Galaxy Watch 6.
I did get some ‘ineligible’ error messages from Telstra but it all worked anyway.