I am by no means an expert on all things Dolby so I can only tell you my experience.
Yes you have to install the "free" Adobe Access App from the windows app store. Then you have to "Subscribe" for the right to unlocking ATMOS capability on the APP. (This is a Dolby thing so don't blame Logitech). When I did this a few months ago, the first year was free, then each year was something like $10-$15. Some of the headset makers are including a free coupon for an extra year. One nice thing is that the app works across multiple platforms with the same subscriptions (at least PC and XBOX is what I have).