Can I connect an external Bluray drive to a laptop DVD drive?
If you still have a free USB port yes
You can't connect anything to the DVD drive, you can only insert a DVD.
External drives are connected via USB.
External Bluray drives are usually connected via a USB port.
With some devices you can retrofit a corresponding drive more or less easily. Simply google the device name in connection with the keywords "replace optical drive", and at the same time again search for a suitable bd drive for your device.
if you do not find anything suitable or you are not sure, you can always connect an external drive to one of the free usb ports.
https://www.alternate.de/html/product/993845
there are also cheaper at wish or aliexpress. But frankly I'm not sure if you can get what you expect.