Now then. Briefly, when I set up my current new PC I had it one a cloud (i.e. Microsoft) account. ( Just rushing the set up process a bit).
And I couldn't get the shared folders to be, err shared or even seen on my other PCs.
Not, that is, until I put it on to a local account, which is what my other PCs are on. At which point the shares magically appeared.
So while I was already pretty resistant to letting Win 11 on to this nice shiny new computer there is absolutely no way I will let it on if there is any chance of it buggering up my shared areas..