Hi, Barney. Thanks for the reply.
I think i'm either missing something obvious or not understanding.
On my old iMac running Mojave, i can go to my Macintosh HD/internal SSD/boot drive. I can add a folder, copy something onto it—whatever. It will tell me i need to enter my password to do this, but i can do it. When i select that drive from my finder sidebar and do Get Info, in sharing & permissions, i see System, Wheel, and Everyone. System has Read & Write, the others have Read Only.
When i do the same on my new Mac Studio, i see the same in Get Info. But, i cannot do anything on that drive.
In 30 years of Mac use, i don't think i've ever used a HOME folder! There are things in there, but i think they've been added by various processes and apps. I don't ever manually put things there. I guess i'll start now. But, i'm wondering if this permissions thing is new to OSs later than the Mojave i've been using? Or if there's something wrong with how i migrated and set up this new machine.