That is new "state of art" way to protect user from malicious drivers. Or to be honest, very good way to get more money. Because certificates have expiration date. You know, after some period drivers turn bad....
And you pay about 200-500$ per year to maintain drivers signed and to redistribute new signed driver every 1 to 3 years.
You have option to get 32bit version, and then it shouldn't disable unsigned drivers, go back to win 7, or pay to sign driver...
Even if original driver is signed, they probably changed PID and VID for Amicus, so that render driver useless.

There is one more option, but probably wont work.
You can try to manually force FTDI driver to Amicus.
1. Uninstall all drivers for Amicus.
2. When you plugin USB cancel automatic search.
3. Go to device meager right click properties, go to driver tab, click update driver
4. Let me browse option, Then select from list, or what ever is called on win10
5. Then click to have disk, select FTDI signed drives files.
6. Click what ever is needed to install it. You should get some errors that driver isn't compatible, etc...
This you may expect with all drivers stored on disc. So you need always to have new signed driver. Or at least every couple years.
I have this issue with microchip drivers for my devices. I have CDC on couple devices and just changer PID and VID to match with PID and VID in device, and that makes driver unsigned. And you also need to pay VID to USB...
Also there is some changes in CE certification for EU. So it seems that small manufacturers have no chance....
Hope that this help you.