Dear Leon,
Thank you so much for your reply!
On your computer, press the Windows key + R, type "msconfig," and then click on Boot. On the Boot page, check if it shows one or two Windows installations. If it shows two Windows installations, try changing the Timeout from zero to 30 seconds, then click Apply and restart your PC. Check if you are able to see both Windows installations.
If it still shows only one Windows installation, please send me a screenshot.
Warm Regards,
Arif