In my case, I haven't initiated the Family subscription: I'm simply having difficulty trying to join one.
When I posted earlier tofay, I had been experiencing that same as OP experienced: "The instructions to download it are woefully inadequate. I keep getting sidetracked to requirements that are either out of date or do not work."
For example, I was invited to Register my Device - which is both a red herring, and not actually possible in my case.
Eventually, I stumbled on a page where I could download the Microsoft 365 software to my fairly-new Macbook. But it turns out that Microsoft 365 won't run on it, because its macOS is unsupported by Microsoft.
So the best advice I've found since posting is to risk upgrading my macOS - and it is a risk, because doing that will disable some apps from other sources.
I will give that a try, but frankly my Family now look likely to cancel the 365 subscription as being more trouble than it's worth
(Last time I used Microsoft Office, I was able to do so for eleven years - the whole lifetime of that PC from initial delivery to finally catching fire.)