Hi Corny99, I am Rob, an independent and a 10 time and dual award MVP specializing in Windows troubleshooting and Bluescreen analysis. Please remember as independents we are not responsible for the development of Windows or the computer hardware and drivers.
You can put 4,294,967,295 files into a single folder if drive is formatted with NTFS (would be unusual if it were not) as long as you do not exceed 256 terabytes (single file size and space) or all of disk space that was available whichever is less.
For older FAT32 drives the limits are 65,534 files in a single folder and max file size of 4 Gigabytes and 2TB of total space or all of disk space that was available or whichever is less.
Please let us know the results and if you need further assistance.