Hi, I'm Rodrigo and I will help you.
I understand the files from the Lenovo laptop are showing on the Dell desktop.
To avoid this, you can disable the OneDrive backup feature, which is syncing both device user folders.
Right-click the OneDrive icon on the right side of the taskbar (cloud icon) > Settings > Sync and Backup > Manage Backup > Turn off all folder options > Save changes.
The files will disappear, but they are on the OneDrive folder, if you need any file, you can find it there and copy/move to the location you want.