Almost. I started my island on my regular switch, but then managed to get an AC version too. I synced my user data on the new one, and downloaded ACNH but then I decided not to play it.
This was for two main reasons. Valenwood will always be my "main island" and I'm hoping down the line that Nintendo will allow save transfers so I can move Valenwood to my new AC switch... It sounds daft but it's just how I would prefer it.
Also, as I am not TT'ing in Valenwood, I have so much left to discover and I kinda want to keep that as pure as possible. I feel if I add a second town at this point, it will dilute my experience and I'd rather give 100% to one town until I am further along.
I had 10 NL carts at one point, so it's pretty certain I will have another town at some point... just for me, now isn't the right time.
I do wish you all the luck with two islands, and hope it works out really well for you