Unwanted copying of data from external to internal memory

I have just moved into my firstMac, a Mini M4 24GB UM, 512GB Internal plus a 2TB External SSD running Tahoe. I moved my data manually, placing a big folder of image files and a 20GB folder named myDocuments which is by it's nature a bit of a ragbag, containing assorted document files and associated images.

All apps present are fresh installations. I put Photoshop and Lightroom in their own folder entirely separate from Mac Photos as I envisaged possible file ownership and catalogue issues. So far this has been successful.

Yesterday I added an external HDD for Time Machine and created my first backup - and then decided to have a bit of a look round and check that all was neat and tidy - that was when I realised that the entire contents of 'myDocuments' had been copied into 'Documents' on the internal drive. (I verified that by dismounting my external drive and opening a few files!)

I was aiming for a fairly traditional configuration - data stored externally, apps installed internally, with the rest of the internal 'space' available as a working area. That may seem excessive, but some of the functions Adobe includes these days are resource hogs, so there's future proofing to consider!

Basically, I don't want these files on the internal disc. I thought that giving my created holding folder a unique name would be enough to keep them distinct. It wasn't, so presumably if I just delete the contents of Documents, they will soon reappear... So what should I try next, Please?