Migrating system folders from external drive to new iMAC

After recently purchasing a new Mac Studio, I used Migration Asst to transfer files from my 2011 iMAC. The old mac had a smaller SSD to run the OS, and an HDD I used to store less frequently used system files, including "Documents,""Movies," "Pictures," etc.

As the new Mac Studio has plenty of storage on a single SSD, I was anticipating everything would seamlessly merge from the old SSD+HDD to the new SSD using migration assistant. With the same UserID, it didn't work that easy. The new iMAC studio is using the old HDD as a remote server from my old CPU. This setup isn't a long-term solution given the age of the old iMAC since the new Mac is accessing the old. Coping/cutting or dragging/dropping the folders in Finder from the old HDD to the new SSD doesn't work. Am hoping to avoid setting up the Mac Studio as a new user, but perhaps that's the only option. If there's something easy I'm missing, hoping the group can assist.

How do I reassign these system folders from the old HDD on my old iMAC to the new SSD on my new MacStudio?