First of all, Daz 6 is officially
DAZ 2025 ALPHA (like
anne O'nymous already mentioned) and it will appear in your DIM (if you're logged in) - Mines been waiting there since April, for me to try it.
Second of all... DIM is usually downloaded directly from your DAZ account. In fact, I saw the link for it there just a few days ago when I was on the DAZ website trying to troubleshoot a database issue I was having. It was on the page that shows any bought assets you have (The order page I think) And for as long as I have used DIM, it was always able to be run Offline. I usually just dump the IM000xxxxx.zip files directly into the DIM download folder to install them offline.
But you do need to log in to download any purchased assets and also for some few other scenarios. Like, for example, my DB issue the other day. I couldn't re-import the metadata for the ~1000+ assets I have until I logged in. I logged in, the DB updated in 20 seconds or so, then I logged out again. DAZ doesn't care if half my shit is pirated. They know the vast majority of users are doing that. I pirate basically everything at first, to try it, and then if I decide to use it in one of my paid projects, I buy it.