love to see a picture of disk management, I could guess the efi is on ssd and windows might be booting from hdd
Either case, since both new installs, remove the drive you don't want win 10 on and reinstall on other drive. once it boots without any problems, then add old drive and make sure its not added to boot order.
1. simplest way to delete 2nd install is use diskpart, no need for extra software
Boot from installer
On screen after language choice, pick repair pc, not install
Pick troubleshoot
Pick advanced
Pick Command Prompt
Type diskpart and press enter
Type list disk and press enter
This will show the list of drives currently attached to PC, make note of the drive number of the drive you want to wipe
If Disk 1 is the drive you want to clear, type select 1) and press enter. A message will confirm it is selected
Warning: Diskpart Erase/Clean will permanently erase/destroy all data on the selected drive. Please be certain that you are erasing the correct disk.
Once you sure its right disk, type Clean and press enter
The Command Prompt window will display the message "DiskPart succeeded in cleaning the disk". Close out of the Command Prompt window by clicking the red X in the upper right hand corner.