I am sure that in the Bluetooth standard there are no restrictions for the simultaneous use of both conventional and LE-connections (on the host side).
However, I think that there may be a limitation on the fact that on the same device at the same level there is both a regular and LE connection. However, there is no reason for this, since all LE features are available through a regular Bluetooth connection on devices with both capabilities.
EDIT:
You can restrict the device to not allow both LE and BR / EDR, or you can also enable it. I'm not sure why you want to connect both on one device.
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