You’re mostly correct. You don’t have any choice right now. There is no Logic ARM currently. (Although I assume that will change before they deploy to retail.) When you double-click the Logic icon, it is an Intel version running in Rosetta2. It can load Intel plugins.
When you get the UB version of Logic, it will only run ARM plugins, unless you specifically order it to run in Rosetta2 (there will be a checkbox in the get info panel), in which case it will only run Intel plugins. This will be the same for any host that does not have a separate process for plugins. So basically any of the major hosts except Bitwig. I expect that Bitwig will be able to run both Intel and ARM plugins.
Assuming this goes about like the PPC->Intel switch did, you’ll get about 6 months worth of very confused customers, then shit will settle out, and after about 3 years of it, you won’t have to build Intel plugins any more.